Psoriasis is characterized by hyperproliferation and abnormal differentiation of keratinocytes, and inflammation. 1,25-Dihydroxyvitamin D3, which is used for the treatment of psoriasis, binds to vitamin D receptor (VDR) and modulates gene transcription. We analyzed VDR gene FokI, ApaI and TaqI polymorphisms in 51 Turkish familial psoriasis patients (psoriasis vulgaris and psoriatic arthritis) and 100 healthy subjects, and evaluated the correlation between VDR genotypes and calcipotriol response. We found that the TT genotype was significantly more frequent in the patients than in the controls (51 vs. 35%: P < or = 0.05). The frequency of the T allele in patients was also significantly higher than that in the controls (73.5 vs. 59.5%: P < or = 0.025). In psoriatic arthritis patients, T allele frequency was even higher (91.7%: P < or = 0.05). With regard to response to calcipotriol treatment, in nonresponsive patients TT genotype and T allele frequencies were higher than they were in the controls (63.6 vs. 35%: P < or = 0.025, 81.8 vs. 59.5%: P < or = 0.01, respectively). In conclusion, we show that VDR gene TaqI polymorphism is associated with familial psoriasis in the Turkish population. We also demonstrate that VDR gene polymorphisms may play a role in partial resistance to calcipotriol therapy.