We describe a brother and sister with amelogenesis imperfecta, nephrocalcinosis and impaired renal concentrating ability. This is the second sibship reported, further substantiating autosomal recessive inheritance of this condition. There is lack of enamel, lifelong nocturnal enuresis, progressive punctate nephrocalcinosis, and decreased calcium and phosphate excretion over 24 hours and after an acute load. Increased serum osteocalcin and decreased urine delta-carboxyglutamic acid suggest involvement of vitamin K-dependent calcium binding proteins, although this may represent a secondary finding. No other evidence of abnormal calcium metabolism was found. Renal function is stable in the early teens, but the previously reported patients went on to renal failure.