Simple multicystic dysplastic kidney (MCDK) disease, defined as unilateral MCDK without other genitourinary tract involvement, portends an excellent prognosis. Nevertheless, its long-term management remains undefined. This study aims to provide subspecialty discharge recommendations for these patients. We identified eighty patients with simple MCDK disease by renal ultrasound between 1996 and 2006. Their charts were reviewed for growth of the contralateral kidney, involution of the MCDK, and incidence of complications, specifically hypertension, chronic renal insufficiency (CRI), urinary tract infection (UTI), and malignancy. Mean follow-up was 5 years. At approximately 1 year, 59% of unaffected kidneys were hypertrophied (>or=95th percentile for age/height) and 100% were >50th percentile. With continued follow-up, 80.3% of unaffected kidneys were hypertrophied. Likewise, at 1 year, 71.2% of MCDKs assessed were either involuting or had disappeared; on further follow-up, this increased to 89.6%. No patient had hypertension, CRI, or malignancy. Four patients (5%) developed nonrecurrent UTIs, none leading to renal scarring or growth impairment. These data suggest that subspecialty follow-up may be discontinued once contralateral hypertrophy and ipsilateral involution occur, assuming that the patient has not experienced hypertension, CRI, or UTI. These criteria are often met by 1 year of age, which would preclude repeated visits, uncomfortable investigations, and unnecessary costs.