Clinical findings, management, and possible linkage of congenital hydronephrosis caused by ureteropelvic junction stenosis to the HLA complex were studied in four families. These families provide evidence of possible autosomal dominant inheritance. HLA class I antigen studies in all four and class II (HLA-DR) in three families were performed. These studies failed to show close linkage to the chromosome 6 markers in two families but there was consistent inheritance in the other two. Although formal linkage calculations are not presented, it is apparent that in some families HLA haplotyping is not useful in predicting prevence of renal obstruction.