The aim of this study was to determine the frequency of mutated allele CYP2D6*4 in the Turkish ankylosing spondylitis (AS) patients and healthy controls. Hundred unrelated AS patients who were diagnosed and treated in the Physical Medicine and Rehabilitation Clinic of Ankara Numune Research and Training Hospital and 52 healthy control subjects were included in the study. The wild-type allele of CYP2D6 and the mutated allele CYP2D6*4 were detected by polymerase chain reaction and a subsequent hybridization reaction. CYP2D6*4 allele was not detected in 72 subjects (72%) of the AS patients. Among the remaining 28 patients, 7 (7%) were carriers of two *4 alleles, being homozygous for CYP2D6. Twenty-one patients (21%) were carriers of one *4 allele, being heterozygous for CYP2D6*4. Among the healthy control subjects (n = 52), 23% were heterozygous and 2% were homozygous for CYP2D6*4 polymorphism. The frequency of the CYP2D6*4 allele was 0.175 in the AS patients (100 patients; 200 alleles). The frequency of the CYP2D6*4 allele was 0.134 in control group (52 control subjects; 104 alleles). The odds ratios for development of the AS for the presence of one or two CYP2D6*4 alleles with no CYP2D6*4 alleles as baseline were calculated. No significant risk of AS development was observed for individuals with one or two CYP2D6*4 alleles. Findings of this study showed no significant association between CYP2D6*4 allele and AS in our population. Further studies with larger scaled groups should be performed.