Likelihood analysis using two autosomal/X-linked mixed models confirmed that Alport syndrome is an X-linked dominant disease in a large Utah kindred, family P. The penetrance was estimated as .85 in females and 1.0 in males. Previously reported abnormal segregation ratios were reexamined. No excess of affected offspring of affected parents was found. Nor was the penetrance in daughters of asymptomatic carrier mothers found to be lower than in the daughters of symptomatic mothers, although the sample size was small. However, there was an unexplained deficiency of sons of affected fathers. There was no deficiency of sons of affected mothers, nor was there a deficiency of males in the kindred.