To elucidate the association between killer cell immunoglobulin-like receptors (KIRs) and psoriasis vulgaris (PV), we typed 14 KIR genes in 96 Japanese cases and 50 healthy controls using PCR with sequence-specific primers (PCR-SSP). Here we report an interesting association between certain KIRs and Japanese cases with PV. The frequencies of KIR2DS1 and KIR2DL5 were significantly increased in PV cases compared with controls (KIR2DS1, 43 of 96 (45%) in cases vs 14 of 50 (28%) in controls; KIR2DL5, 46 of 96 (48%) in cases vs 15 of 50 (30%) in controls, p<0.05 for both), and the frequency of carriage of at least one presumed "B" haplotype, inferred from patterns including KIR2DL2, KIR2DL5, and/or various combinations of activating KIRs, was also statistically increased in the PV cases (53 of 96 (55%) in cases vs 18 of 50 (36%) in controls, p<0.04). The increase in KIR2DS1 has also been observed in psoriatic arthritis, another HLA-Cw6-associated disease (Martin et al, 2002). Accordingly, KIR2DS1 may be a common denominator of both diseases.