The aim of this study was to assess the role of HLA-B*27 and it's subtypes in determining severity and clinical manifestations of ankylosing spondylitis (AS).A total of 163 AS patients were assessed for clinical manifestations and severity using structured questionnaires. HLA-B*27 screening and B*27 sub-typing were performed by PCR.One hundred twenty two patients (74.8%) were B*27 positive. The male to female ratio, peripheral arthritis, steroid use, intense dorsal kyphosis and decrease of cervical slope had a significantly higher frequency in B*27 positive patients compared to B*27 negative ones (p=0.01, 0.001, 0.01, 0.04 and 0.04, respectively). However, the age of diagnosis was significantly lower in B*27 positive patients (p=0.005). Trend in uveitis and some severity markers including: BASMI and ASQoL were toward higher values in B*27 positive group with no significant difference. After controlling confounding variables, significant relationship was found only between B*27 and BASMI (p=0.01). B*27 subtypes in patients were included B*2705: 48.4%, B*2702: 42.6%, B*2704: 5.7% and B*2707: 3.3%. No significant differences were seen for severity markers and clinical manifestations between subtypes; although trend toward lower values of severity markers, less intense dorsal kyphosis and less decrease of cervical slope were observed in B*2704 and B*2707 versus other polymorphisms.Clinical features and severity of AS is influenced by HLA-B*27. Trend toward higher severity markers in B*2705 and B*2702 versus other polymorphisms might be subject of interest for evaluation in other ethnicities with concentration to other novel susceptibility genes co-inherited in each B*27 subtype.