Prevalence of antibodies to measles and rubella was tested in sera collected from 1368 subjects in urban and rural Sana'a. Overall, 11.7% had no antibodies to measles and 14.6% had no antibodies to rubella, despite the fact that measles but not rubella vaccine is included in the vaccination program in Yemen. Of 89 children <5 years of age 49 (55.1%) had no detectable antibodies to measles, demonstrating that supplementary measles immunization campaigns are required to prevent virus circulation. Assessment of measles immune status among infants in the first year of life is required to determine the optimum age for measles vaccination. Rubella vaccination should be considered with care in Yemen.