Introduction: Understanding patients' self-reported chemotherapy side effects is significant because it affects patients' quality of life (QOL) and compliance with treatment. Our current knowledge of chemotherapy side effects comes from available literature, whose external validity is questionable. Moreover, there are very few studies available in the literature that focus on various cancers and their associated side effects.Methods: A single-center, prospective observational study was conducted at a tertiary care center from July 2019 to July 2021. After deriving the sample size, we interviewed 76 consecutive study patients with gastric, periampullary, colorectal, and breast cancer for six months after chemotherapy initiation with a structured patient-reported outcome tool adapted in English and Tamil to record the side effects like diarrhea, vomiting, chest pain, constipation, dyspnea, fatigue, mucositis, and rash. The grading of symptoms was done according to the Common Terminology Criteria for Adverse Events version 5.0. The frequency and prevalence of side effects were calculated as the number of patients who reported the side effect of any grade at least once during the follow-up period. The incidence rate of side effects was calculated in terms of person-time. The association between each side effect and cancer type was calculated using the chi-square test and Fisher's exact test as appropriate.Results: Of the 77 patients in the study, 51.9% were male, 63.6% were between 40 and 60 years of age, 45.5% had stage-3 disease, and 44.2% received neoadjuvant treatment. During the six-month follow-up period, 97.4% of patients experienced at least one side effect. Fatigue was the most common side effect (87%), followed by loss of appetite (71.4%) and diarrhea (49.4%). Approximately 66.7% of patients experienced six or more side effects. There was a statistically significant difference in the frequency of side effects between cancer types. However, age, socioeconomic status, BMI, comorbidity, chemo-intent, and stage of disease did not affect the frequency of side effects.Conclusions: This study highlights the need to integrate patient-reported side effects into routine clinical practice. Identifying these side effects, even if they are mild in intensity, and managing them in a timely manner may improve the patient's emotional state, QOL, and compliance with chemotherapy.