Two hundred and twenty patients in one general practice travelling to destinations where immunization against hepatitis A virus (HAV) is recommended were tested for their HAV immune status before immunization. Age-specific prevalence of prior immunity to HAV was estimated. The relative costs of pre-immunization testing and immediate immunization were compared. The most cost-effective testing method for this practice was found to be total population testing prior to immunization with HAV vaccine. Individual general practices can estimate the optimal age at which to commence testing for HAV in their own practice population.