The Laurence-Moon-Bardet-Biedl syndrome (LMBB) is characterized by the association of obesity, hypogonadism, polydactyly, mental retardation and pigmentary retinitis. Symptomatic or asymptomatic renal dysplasia (calyceal diverticula, precalyceal tubular ectasia, cysts) is frequently associated with LMBB. The authors consider renal sonography as the convenient investigation for an early detection of such dysplasia as in the case they reported here.