Accurate, rapid, and noninvasive health assessments are required to establish more appropriate endpoints in mouse cancer models where tumor size is not easily measured. We evaluated potential endpoints in mice with experimentally induced peritoneal lymphoma, an abdominal tumor model, by comparing body weight, body condition, and behavior with those of a control group of mice not developing lymphoma. Our hypothesis was that body weight would increase or plateau, whereas body condition and behavioral scores would decrease, as disease progressed. Results indicated that body weight did not differ significantly between the control and experimental groups, but the experimental group experienced significant decreases in both body condition and behavioral scores. Our results support the use of body condition and behavioral scoring as adjunctive assessment methods for mice involved in abdominal lymphoma tumor studies in which health may decline despite an increase or plateau in body weight.