Psoriasis vulgaris has HLA associations. We have previously defined HLA-Cw6,DR7,DQA1*0201 as the central element of the risk haplotypes for psoriasis. On the other hand, Cw6 as a single gene has the strongest association with psoriasis. The aim of this study was to determine whether the risk haplotype and Cw6 correlate with the clinical parameters of the disease. The series consisted of 64 patients and the clinical parameters were age at onset, family history of psoriasis, arthritis and the frequency of inpatient treatment. The HLA risk haplotype Cw6,DR7,DQA1*0201 had previously been found in 30% and Cw6 alone in 54% of the patients. The presence of Cw6 correlated with early age at onset (Pc = 0.01). The presence of the risk haplotype correlated with a positive family history of psoriasis among the first-degree relatives (Pc = 0.02) and an overall positive family history (Pc = 0.04), but Cw6 had a stronger correlation with an overall positive family history (Pc = 0.01). There were no positive correlations with arthritis or the number of inpatient treatment periods. Only type I psoriasis was associated with Cw6 (Pc = 0.0006). In conclusion, Cw6 and the haplotype Cw6,DR7,DQA1*0201 are important in the heredity of psoriasis vulgaris, but the presence of Cw6 alone is sufficient to indicate a clinically significant risk for psoriasis.