A previously healthy 12 month old boy presented to hospital with a right 6th nerve palsy seven days after his routine 12 month immunizations: measles, mumps, rubella (MMR) (Priorix®, GSK) and Haemophilus influenzae type b (Hib) – Hepatitis B (Comvax®, Merck). He had been well for the first four days post-immunization, but then noted by his grandparents to have a “squint” and appear lethargic. He presented for medical attention on day seven post-vaccination because of persistent concerns about his unusual eye movements. Two months earlier he had received his second catch-up dose of 7-valent pneumococcal conjugate vaccination (Prevenar®, Wyeth Vaccines) and meningococcal group C conjugate vaccine (Meningitec®, Wyeth Vaccines). He had experienced no adverse events from any of his previous vaccinations, which were up to date for his age on the routine Australian National Immunization Program schedule []. He had a past history of emergency delivery at 36 weeks gestation by caesarean section for twin-twin transfusion following a twin pregnancy conceived by in-vitro fertilization. There were no significant neonatal problems and he was developmentally age appropriate. On admission he was afebrile, blood pressure 117/59, pulse rate 120/min, respiratory rate 30/min and oxygen saturation of 95%. There was no history of preceding viral illness or prodrome and no symptoms developed during admission. Further evaluation by a pediatric neurologist and ophthalmologist confirmed an isolated right 6th nerve palsy, with no evidence of facial asymmetry. There was mild plagiocephaly, with a head circumference of 46.5 cm (50th centile). No ptosis was evident, and fundoscopic examination bilaterally was normal. Initial blood investigations included normal full blood examination (Hb 128 g/L; Platelets 284 x109/L; leukocytes 11.1 x 109/L and normal baseline electrolytes, liver function tests, creatinine kinase (CK) and serum calcium levels. The erythrocyte sedimentation rate (ESR) was normal (3 mm/hr). Neuroimaging with magnetic resonance imaging (MRI) and angiography (MRA) of the brain demonstrated no intracranial abnormality. Cerebrospinal fluid (CSF) examination revealed no white cells, 89 red cells x106/L, protein of 0.19 g/L (0.20-0.40), glucose 2.8 mmol/L (2.8-4.0) and lactate of 1.2 mmol/L. A random blood glucose level was 6.0 mmol/l. There was no growth on CSF cultures. The CSF opening pressure was 31 cm CSF, but this was obtained at the third attempt at a lumbar puncture in a screaming child, and the pressure was therefore likely artefactually elevated. Acetylcholine receptor antibodies were negative (0.2 nmol/L). The differential diagnoses with this presentation included a post viral 6th nerve palsy, idiopathic cranial nerve palsy, myasthenia gravis and benign intracranial hypertension. He was initially trialed on Pyridostigmine (Mestinon® Valeant) 5 mg three times daily. This was subsequently increased to 10 mg three times daily, but with no change in clinical signs it was ceased. The 6th nerve palsy persisted at one-week post vaccination, but completely resolved spontaneously over the next six weeks, with resolution confirmed on ophthalmology follow-up. The child then re-presented aged 20 months with a recurrent episode of a right 6th nerve palsy. On this occasion it commenced followed a different live virus vaccination – Varicella (Varivax® Merck) given four weeks earlier. Again, there was no viral prodrome and he had otherwise been alert and well. He presented with identical symptoms of a squint and was brought to hospital for evaluation five weeks after immunization. Repeat examination by an ophthalmologist and pediatric neurologist again confirmed an isolated 6th nerve palsy with no evidence of papilledema. He was afebrile and haemodynamically stable. The nerve palsy worsened over the subsequent two days, then significantly improved over the next 7–10 days and had entirely resolved by 5 weeks, now a total of 9 weeks post immunisation. On this presentation, he did not have any neuro-imaging, CSF analysis or repeat blood investigations. Over the next 12 months the child tolerated numerous viral infections with no recurrence of the squint or any neurological symptoms. He had ongoing ophthalmology review with no abnormalities noted. A follow-up with pediatric neurology at two years of age confirmed a normal examination, with all appropriate developmental milestones reached. Following detailed discussion with the family it was advised that further live attenuated vaccines not be administered, even though the routine Australian immunization schedule includes a MMR vaccine (2nd dose) at 4 years of age []. The main reason for this advice was that no previous recurrent cases had been reported in the scientific literature and therefore the safety of further live attenuated vaccines in this setting was unknown.