The outcrossing rate of a species is important in designing experiments for inheritance and linkage studies and selection of appropriate breeding methods for crop improvement. Though predominantly self pollinated, frequent heterozygosity was found in isozyme studies grasspea (Lathyrus sativus L.). We established a study to estimate the rate of outcrossing in grasspea. Three planting methods, each with different frequency of the recessive parent, were repeated in three locations. Recessive white flower colour was used as a marker to detect outcrossing. Differences in the frequency of recessive alleles in the different planting methods were accounted in the calculation of outcrossing frequency. The estimates of outcrossing were homogeneous among eight families. The average outcrossing rate was 2.2%. We suggest that seed increases of grasspea be grown under isolation to maintain the genetic integrity of individual grasspea lines.