Coagulation factor V (FV) deficiency is a rare bleeding disorder characterized by low coagulant and antigen levels of FV with bleeding symptoms ranging from mild to severe. Only a limited number of mutations have been reported because of the large size of the factor V gene (F5) as well as the low prevalence. In this study, we have identified four novel mutations in F5 in five unrelated patients with congenital FV deficiency. All the patients, including two with undetectable FV activity, were asymptomatic and were found to have prolonged prothrombin time and activated partial thromboplastin time during preoperative screening or routine examinations. All four mutations found in this study are either missense or in-frame deletion. This is in contrast with previous reports of a high frequency of mutations introducing premature termination codons in inherited FV deficiency. Missense mutations of F5 might produce a mild phenotype and are not frequently diagnosed. Although FV deficiency is a very rare disorder with a predicted incidence of one in 1 million, this study suggests that the numbers of F5 mutations, especially missense mutations, are higher than estimated.