To determine the course of visual functions in patients with Bardet-Biedl syndrome. The 21 patients with Bardet-Biedl syndrome seen at Children's Hospital, Boston, Mass, had optotype and grating acuities and dark-adapted thresholds measured over time. Their ages at first visit ranged from 2 weeks to 23 years (median age, 6 years). The courses of the visual functions were analyzed with a random-effects model. Substantial declines in visual functions were found. On average, grating and optotype acuities declined 0.09 log units (roughly 1 line) per year, and thresholds increased about 0.19 log units per year. The rates at which these visual functions were lost and the predicted level of the visual functions at ages 11 to 12 years (the mean ages of measurement) varied among individuals. The visual prognosis for children with Bardet-Biedl syndrome is poor. The course of both central and peripheral visual functions is variable.