The purpose of this study was to investigate the side-effects experienced by patients with colorectal cancer receiving 5-fluorouracil + folinic acid chemotherapy. A primary objective was to provide quantitative data on the incidence and severity of side-effects at each cycle of chemotherapy treatment. Twelve patients with Duke's B or Duke's C adenocarcinoma participated. Data collection was via a self-report questionnaire listing 61 possible side-effects. Participants completed a questionnaire following each cycle of chemotherapy. The response rate was 100%. Seventy-eight side-effects were reported by the sample. Fatigue was the most common side-effect (incidence = 97%) and achieved the highest C score (59/100). However, patients ranked mouth ulceration as the worst side-effect overall. Several previously unreported problems were identified, including nose bleeding, change in taste and weight loss. Although limited by a small sample size, this study suggests the problems experienced by patients undergoing 5-fluorouracil chemotherapy are many and diverse. It is concluded that investigation is needed into associations between side-effects and the role of patient characteristics in the onset of side-effects.