M.A. / This study investigates the relationship between psychological birth order position, gender and different types and levels of prosocial tendencies in individuals. An ex post facto, between-family research design was used. The Prosocial Tendencies Measure (PTM) which assesses the six types of prosocial behaviours, was completed by eight hundred and eighty-eight participants. Despite the use of specific statistical and methodological procedures to increase sensitivity and reduce error, no significant support was found for the hypothesis that birth order affects prosocial tendencies in individuals on five of the subscales of the PTM. There were, however, statistically significant differences in scores between middleborns and lastborns on the Altruism subscale with middleborns scoring significantly higher than lastborns. Consistent with the hypotheses, statistically significant gender differences were found on the subscales measuring public, emotional, altruistic and compliant prosocial tendencies. The results of the study are discussed in the context of the mixed research findings relating to birth order effects and propose further research into the possible developmental dynamics that may produce greater levels of prosocial tendencies in individuals.