PURPOSE: To describe conceptions, as registered by a semi-structured interview, of exercise as treatment among sixteen middle-aged patients with moderate to severe knee osteoarthritis. METHOD: Sixteen patients (aged 39-64) with symptomatic, radiographic knee osteoarthritis and previous participants in an exercise intervention, were interviewed. The qualitative data obtained were analysed using phenomenographic approach. RESULTS: Four descriptive categories containing 13 conceptions emerged: Category 1) To gain health included five conceptions; to experience coherence, to experience well-being, to be in control, to experience improved physical functioning, to experience symptom relief; 2) To become motivated included three conceptions; to experience inspiration, to be prepared to persevere, to experience the need to exercise; 3) To experience the need for support included three conceptions; to have structure, to receive guidance, to devote time; 4) To experience resistance included two conceptions; to hesitate, to deprecate. CONCLUSION: Patients with knee osteoarthritis and knee pain, previously participating in exercise intervention, are aware of the health benefits of exercise, but have many doubts and concerns about exercise as treatment. These aspects should be considered when designing patient information and treatment programmes. Furthermore, a hesitative and resistive perception of exercise as a concept could have major influences on the implementation of health programmes.