Infection of ewes by Toxoplasma gondii may induce abortions, thus it has consequences for sheep production. Colima, Western State of Mexico, has favourable climatic conditions for transmission and both domestic and wild cats live there. The aim of this study was to determine the frequency of specific antibodies in sheep from the coast, a mountain, and a hill of Colima. Serum samples from 351 sheep were tested by a previously standardized indirect ELISA. The frequency of infection was estimated and the farm location and flock size, as well as the animals' age and sex were analysed as risk factors for toxoplasmosis. The frequency of antibodies depended on the altitude, being higher at sea level than at 1200 metres above sea level (OR=3·77, 95% CI=1·79–7·94, P<0·0001), and the size of the flock, being higher in the large ones (OR=2·23, 95% CI=1·35–3·71, P=0·002). Older animals were more frequently positive and with a stronger response than young ones (OR=1·77, 95% CI=1·07–2·93, P=0·016). No differences were observed between male and female sheep. In conclusion, toxoplasmosis is present in sheep of Colima with variations related to altitude, flock size and age.