Due to the anorexia-cachexia syndrome, cancer patients are already suffering from nutritional problems and weight loss by the time they receive their diagnosis and start chemotherapy. In the oncology outpatient clinic of a Swiss university hospital, patients currently undergo a nutritional assessment and receive individual counselling at the beginning of cancer treatment. This qualitative study explored cancer patients' experiences with weight loss and nutritional problems as well as how they experienced the assessment and the consecutive counselling by nurses. Interviews were conducted with 12 patients and qualitative content analysis was used for data analysis. Results showed that patients barely registered the weight loss and did not interpret it as an early warning signal. Nevertheless, they attempted to improve their nutritional habits soon after diagnosis, prior to receiving any counselling. The patients did not experience the assessment as troublesome. They appreciated the nurses' advice and implemented the suggestions they found appropriate. This study highlights the importance of patient education regarding weight loss and nutritional problems early in the course of an illness. Patients may not be aware of nutritional problems at this early stage and may lack the necessary specialised knowledge. Assessment and counselling provided by nurses offer targeted measures for prevention of malnutrition and weight loss.