This study investigated the influence of plant density on several agronomic traits of four sunflower (Helianthus annuus L.) cultivars grown at Indian Head and Saskatoon, Saskatchewan in the semiarid prairies. At populations of 40 000–85 000 plants∙ha−1, plant density had no significant effect on seed yield. The increase in percentage oil content with increase in plant density (44.3–45.6%) was small but significant. As plant density was increased, days to flower, height and test weight increased while days to maturity, head diameter and average seed weight decreased. Cultivars × density interactions were generally not significant. Environment (five location-years) had a significant effect on all variables, and environments × cultivar interactions were significant for most of these. Results of this experiment indicated that testing of sunflower lines at several locations in the growing area would be necessary for best assessment but one plant density, suitable to that area, could be used.Key words: Sunflower, plant density, seed, oil, seed size, Helianthus annuus L.