PURPOSE: Diarrhea is prevalent in individuals with cancer undergoing chemotherapy and negatively affects their outcomes, treatment adherence, and survival. With the majority of patients receiving chemotherapy in an outpatient setting, treatment-related toxicities, including diarrhea, are experienced while at home, and, therefore, their prevalence, frequency, and associated distress remain largely uncaptured. This study aimed to assess the prevalence and severity of patient-reported diarrhea and the relationship between diarrhea severity and its associated distress. METHODS: We performed a secondary analysis of diarrhea severity and associated distress ratings (1-10) reported over the course of chemotherapy by individuals with various types and stages of malignancies. Symptoms were assessed daily through an automated telephone system. RESULTS: Out of 345 participants, 217 (62.90%) reported at least one episode of diarrhea. Of the reported diarrhea occurrences, 60.39% were classified as mild (1-3), 34.62% as moderate (4-7), and 4.99% as severe (8-10). The mean duration of mild, moderate, and severe diarrhea was 3.57, 4.84, and 1.43 days, respectively. Of all diarrhea episodes, 97.40% were reported between cycles 1 and 8, with cycle 1 having the greatest number of reported episodes. Out of these, cycle 5 had the highest average diarrhea severity (4.02) and cycle 8 the lowest (2.98). The average number of diarrhea reports per patient was 4.94 for participants in mild symptom group, 3.98 in moderate, and 1.78 in severe. A simple linear regression revealed a significant beta of 0.91 (p <
0.001) between diarrhea severity and the associated distress score. CONCLUSIONS: Diarrhea affected over 60% of study participants. Its severity was highly correlated with patient-reported distress. Clinicians need to be aware that diarrhea can significantly disrupt patients' wellbeing and make it a priority of patient education and post-treatment assessment.