Objective: The distribution of plasma total homocysteine concentrations in a population of South West of Iran Shiraz is described to test for differences in homocysteine concentrations among gender and age groups and those levels reported in other populations.Design and methods: Two hundred one healthy males and 201 healthy females aged >15 years from Shiraz, Iran, were randomly selected. Plasma total homocysteine concentrations were measured using high-performance liquid chromatography.Results: The mean plasma homocysteine level was significantly higher in men (geometric mean, 7.3μmol/l) than in women (geometric mean, 6.3μmol/l, P < 0.001). The geometric mean levels for ages 15-25, 26-36, 37-47, and 48-58, 59-69, and 70-80 years, were 5.9, 5.4, 5.2, 6.7, 7.3, and 7.6 μmol/l in women and 7.5, 8.7, 5.9, 5.9,7.2, and 9.1 μmol/l in men, respectively.Conclusions: The homocysteine distribution in a representative sample of people of southwest of Iran indicates age and gender differences, as is found in other populations.