OBJECTIVE: To determine the frequency of factor V leiden mutation. DESIGN: Observational study. PLACE AND DURATION OF STUDY: One-year, January 2001 to December 2001 at the Armed Forces Institute of Pathology, Rawalpindi, Pakistan. PATIENTS AND METHODS: Two hundred subjects each of apparently healthy and unrelated Punjabi and Pathan origins were included in the study. Peripheral blood samples were collected in EDTA and DNA extracted by phenol-chloroform extraction method. DNA analysis was done by PCR for restriction fragment length polymorphism. The product was digested overnight with Mn/1 and electrophoresed on acrylamide gel to detect 67 and 153 base pair fragments of factor V leiden against 37, 67 and 116 base pair fragments of normal factor V. RESULTS: In the 400 subjects studied, only 5 cases of heterozygotes for factor V leiden were detected. The overall carrier rate was 1.3% (95% Cl 0.2-2.2%). The carrier rate in Punjabis and Pathans was 1% and 1.5% respectively. CONCLUSION: This study confirms that the prevalence of factor V leiden is low in Asians and Africans as compared to the European population.