Records on body mass and reproductive performance of 920 Sussex type cows, ranging in age from yearlings to adults (5 years and older) were examined for relationships between body mass (X) and conception (Y). The data was obtained over a 6-year period and included: body mass at the start and at the end of the breeding season, percentage gain in mass over the mating season, body mass at the start and at the end of the winter and percentage gain or loss over the winter. Significant relationships were recorded for body mass at the start of the mating season and conception for nearly all the age groups with the exception of the 2-year old animals mated for the first time. No relationship could be established for conception rate and mean body mass at the start of the winter, end of the winter, percentage gain or loss over the winter and percentage gain or loss over the winter and percentage gain over the breeding season.