To determine the frequency of factor V leiden mutation.Observational study.One-year, January 2001 to December 2001 at the Armed Forces Institute of Pathology, Rawalpindi, Pakistan.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.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.This study confirms that the prevalence of factor V leiden is low in Asians and Africans as compared to the European population.