The aim of this work was to investigate HLA phenotype predisposition to posttransplantation diabetes mellitus (PTDM) in kidney transplant recipients stratified according to kidney failure etiology. Ninety-eight transplant recipient pairs with kidney grafts from the same cadaveric donor were qualified for the study. In each pair, 1 kidney was grafted to an individual with autosomal dominant polycystic kidney disease (ADPKD group) and 1 to recipient with a different cause of kidney failure (non-ADPKD group). All class II HLA antigens were determined with the PCR-SSP molecular method. To identify class I HLA molecules we used both molecular and serologic methods. Diabetes was diagnosed according to the American Diabetes Association criteria. The posttransplantation observation period was 12 months. In the ADPKD group, HLA-B27 was more common in PTDM than non-PTDM patients; 31.6% versus 11.4% (P = .069). The difference achieved significance when comparing insulin-treated with non-insulin-treated patients (44.4% vs 12.4%; P = .029). In the non-ADPKD group, HLA-A28 and HLA-B13 were observed more frequently in patients with PTDM than in recipients without diabetes (22.2% vs 2.5% [P = .0099] and 22.2% vs 3.8% [P = .020]). All of these associations were significant upon multivariate analysis. HLA-B27 allele is a factor predisposing ADPKD patients to insulin-dependent PTDM. Antigens predisposing to PTDM among kidney graft recipients without ADPKD include HLA-A28 and B13.