We report a case of transitory hypertension associated with unilateral multicystic dysplastic kidney (MCDK). A newborn girl with MCDK, detected by prenatal ultrasonography, was conservatively treated and has been followed for 18 months at the Pediatric Nephrourology Unit (HC-Belo Horizonte, Brazil). Arterial hypertension was observed at about 4 months of age and was associated with high levels of plasma renin activity and circulating angiotensin, and also with changes in renal Doppler ultrasonography. For these reasons, a nephrectomy was initially proposed. However, a spontaneous improvement of blood pressure levels was noticed at about 10 months of age. Serial Doppler ultrasonography showed involution of the affected renal volume and decreased arterial flow. The anatomical improvement was observed simultaneously with normalization of the peripheral renin and angiotensin values. The literature is reviewed regarding the relationship between hypertension and MCDK.