The Bardet-Biedl syndrome is characterized by five main features: obesity, polydactyly, pigmentary retinopathy, mental deficiency and hypogonadism; recently a sixth feature, renal disease, has been described. It was formerly known as the Laurence-Moon-Biedl syndrome, but Laurence and Moon described a different entity in which the main feature was paraplegia. Fourteen cases have been seen: all had pigmentary retinopathy which, in most cases, was severe and tended to affect central vision early in life. All had subnormal intelligence, twelve were obese, ten had polydactyly, eight hypogonadism, and two had renal disease. The condition was thought to be rare, but this may have been due to the failure to diagnose incomplete or partial cases. It is suggested that the prevalence is 1:160 000 of the population.