The volume of the cerebellum as a whole and the volume of the molecular layer per Purkinje cell in adult tottering (tg/tg) and tottering/leaner (tg/tg(la)) mice were reduced when compared with normal age-matched wild type mice (+/+). No changes in the volume of the granule cell layer or white matter layer were detected, suggesting that the mutation effects were limited to the molecular layer of the cerebellum. The density of Purkinje cells and the total number of Purkinje cells did not vary between groups. The cerebellar and body weights were decreased in tg/tg and tg/tg(la) mice compared with +/+ mice.