The purposes of this study were to identify the number and types of symptom clusters using yes/no responses from the Memorial Symptom Assessment Scale, identify the number and types of symptom clusters using severity scores from the Memorial Symptom Assessment Scale, compare the identified symptom clusters derived using severity scores to those derived using occurrence ratings, and evaluate for differences in symptom cluster severity scores between patients with breast and prostate cancer at the end of radiation therapy. Separate exploratory factor analyses were performed to determine the number of symptom clusters based on symptom occurrence rates and symptom severity ratings. Although specific symptoms within each symptom cluster were not identical, 3 very similar symptom clusters (ie, "mood-cognitive" symptom cluster, "sickness-behavior" symptom cluster, "treatment-related" symptom cluster) were identified regardless of whether occurrence rates or severity ratings were used to create the symptom clusters at the end of radiation therapy. However, the factor solution derived using the severity ratings fit the data better. Significant differences in severity scores for all 3 symptom clusters were found between patients with breast and prostate cancer. For all 3 symptom clusters, the patients with breast cancer had higher symptom cluster severity scores than the patients with prostate cancer.