Phenotypic effects and transmission rates of the extra chromosome in interspecific trisomics of Cucurbita moschata cv. Butternut (2n C. moschata + 1 C. palmata chromosome) were compared with those of a primary trisomic of C. moschata. Based on gross morphological similarities, 17 interspecific trisomic lines were placed in six phenotypic groups, suggesting that six different C. palmata chromosomes were recovered. Fruit from one of the interspecific trisomics exhibited the hard rind of C. palmata, indicating that this is a dominant trait carried on one chromosome. Some phenotypic effects of the extra chromosome were similar in both the interspecific and primary trisomics, showing a chromosomal effect due to genic imbalance. Transmission of the extra chromosome through the female ranged from 15% to 32% for the C. palmata chromosomes, and was 44% in the primary trisomic. None of the extra chromosomes were transmitted through the male parent.