Objectives: To assess outcomes of unilateral multicystic dysplastic kidney (MCDK) managed at an Australasian centre over a 15 year period. To assess if MCDK involution could be predicted based on change noted between first two postnatal ultrasound scans 6 months apart. Subjects and Methods: A retrospective study was performed. Results: One-hundred-and-six cases of unilateral MCDK were studied. Eighty-four of these presented antenatally. Twenty-two MCDK cases presented postnatally. Urological anomalies associated with MCDK included vesicoureteric reflux (VUR), ureterocele and contralateral pelviureteric junction obstruction (PUJO). Children undergoing surgical intervention for these anomalies were offered concurrent MCDK nephrectomy. Morbidity associated with MCDK under surveillance included febrile culture-positive urinary tract infection in 20 cases (20.7%), hypertension in four (3.7%) and Wilms' tumor in one (0.9%). Thirty-six cases (34%) underwent complete involution, 32 (30.2%) were in the process of involuting and 38 cases (35.8%) underwent nephrectomy because of failure of involution or associated morbidity. If the MCDK reduced in cranio-caudal interpolar length by 20% or more between the first postnatal USS and the next one 6 months later, then it was very likely to involute spontaneously. If the MCDK did not reduce in cranio-caudal interpolar length by 20% between the first postnatal scan and the next one 6 months later, then it was highly likely to fail to involute, and in our study, correlated with the outcome of nephrectomy. Conclusion: Although MCDK is a benign condition, it should be carefully investigated and followed-up, as involution may not occur in over a third. In some cases, morbidity may occur. Each case of MCDK should be managed on its own merits. Level of Evidence: Level II – Prognosis study, Retrospective.