The oldest members of most short- and long-lived mammalian species develop many similar morphologic changes. This suggests that the combined occurrence of a variety of age-associated lesions in a group can be used as an indicator of its advanced biological age. Males and females from our colony of aging Syrian hamsters were previously shown to have an equally high incidence of atrial thrombosis and myocardial degeneration, despite the females' much shorter life-span. Other age-associated lesions were then examined histopathologically to determine whether females age faster than males. Hepatic, renal, and splenic amyloidosis were more severe in females than in males and became so at an earlier age. Degenerative lesions were also found in adrenals, thyroids, and brains of both sexes. Atrophy was especially severe in the thymus. The incidence of malignant neoplasms, most of which were of lymphoreticular origin, was similar in both sexes. Female hamsters may age faster than males if biological age can be assessed by these morhologic criteria.