Patients undergoing outpatient cancer treatment experience a multitude of therapy-related symptoms. Complete assessment of these symptoms is essential for proper interventions to be provided and to enhance the quality of life of the patient. The primary purposes of the study were to compare the number of symptoms identified by a self-report instrument with those documented in the patient's medical record, and to examine the relationship between the number of self-reported symptoms and quality of life. Ninety-one oncology patients from three outpatient clinics participated in the study. The Oncology Treatment Toxicity Assessment Tool (OTTAT) and the Quality of Life Index (QLI) are self-report instruments, each with 37 items and 18 items, respectively. The mean number of symptoms reported on the OTTAT (mean = 11; range 0–37; SD 8) was significantly higher than that documented in the medical record (mean = 1.5 range 0–9; SD 1.6), (t = 8.7, p = 0.001). Higher scores on the OTTAT were significantly related to lower scores on the QLI (r = −0.67, p = 0.0001).