A 79-year-old male retired veteranarian from Semnan province, living in Tehran, was referred to a non-academic private nephrology clinic due to slightly elevated creatinine levels and flank pain at 2012. He had hypertension and coronary artery stenting. He was under treatment with aspirin and metoprolol. In 2005, he had presented with generalized itching and a skin lesion on his left leg, which was non-significant on biopsy and resolved without any special treatment. He was totally asymptomatic until 2012, when he was admitted at a private clinic hospital in Tehran, for intermittent right flank pain without urinary symptoms. Ultrasonography revealed cysts in the kidneys. Four cysts with the largest diameter of < 3 cm and one cyst of 36*49 mm size with multiple septa in right kidney were visualizied. There were four cortical cysts in the left kidney with a maximum diameter of 28 mm. The patient had been discharged with the wrong diagnosis of bilateral simple cysts and was advised for continuation of follow-up. After 3 years, the patient presented at our hospital for the first time with acute-onset severe right flank pain radiating to groin which lasted for 6 h. He also complained of nausea, vomiting, hematuria and passage of small, white, balloon-like, and grape-size structures in urine. Laboratory findings were listed in Table. The kidneys were examined by ultrasonography and there were some cortical cysts in the left kidney with a maximal diameter of 33 mm and fine calcified septa in one cyst. There was also a solid mass containing small cystic regions with the size of 60*74 mm in lower pole of right kidney with external extension and no vascular flow on color Doppler ultrasonography. The bladder was reported to be normal. Since a complicated cyst was suspected, further investigations were performed. In CT scan, a 70*50 mm multiloculated cystic lesion with multiple non- enhancing internal septa resembeling walls of doughter cysts in mid portion of right kidney was reported. The pathological assessment of balloon-like structures in urine revealed that they were highly suggestive of hydatid cyst. Pathological evaluation showed a laminated cyst wall, partially lined up by a layer of germinal cells. In serological assessment, there were weakly positive results in two laboratory assays by ELISA with a five-month interval. Due to the diagnosis of active hydatid cyst, surgery was recommended but the patient refused surgical treatment. The reason for refusal was the patients’ severe fear of undergoing surgery. Then praziquantel 800 mg three times a day and albendazole 400 mg three times a day were initiated for the patient. Follow-up was recommended. Fourteen months later, while under treatment, he was presented with hydatiduria. Pathology again confirmed the diagnosis of hydatid cyst. With recurrence of hydatiduria, surgical treatment was offered to the patient again, but he refused and medical treatment was continued. Around 12 months later, the hydatid cyst serology turned negative and after 3 months, he was recommended to stop the medications. The concurrent complete blood count, liver function tests and urinalysis were normal. Nine months after cessation of medical treatment, ultrasonography showed a hetero-echo exophytic mass in the right kidney with a size of 58*42 mm. There were cortical cysts in the left kidney in the middle-lower region with the maximum diameter of 26 mm. The bladder wall was thickened. In CT scan a 60*44*42 mm cystic lesion without obvious internal septa and no enhancement was seen. Calcification in the cyst was observed. Follow-up sonography at the last visit 3 years after discontinuation of medications, demonstrated a 60*40*45 solid-appearance lesion without daughter cyst in mid portion of the right kidney. At last, no clinical symptoms were present and the size of lesion was under control. The lesion was turned into a CE4 lesion from an initial CE2 lesion.