Mental health and quality of life were assessed before and after a one-year exercise and diet intervention among 219 healthy individuals, aged 41-50 years, with elevated risk factors for cardiovascular disease. The participants were randomized to four groups: diet (n = 55), diet and exercise (n = 67), exercise (n = 54) and no active intervention (n = 43). Quality of life was measured with one eight-item scale and two one-item scales. Mental health was measured by the General Health Questionnaire (30-item version). Depression, anxiety, feelings of competence and self-esteem, coping and social dysfunction were measured using subscales of the General Health Questionnaire. Somatic anxiety was measured by the anxiety subscale of the Symptom Check List-90. Exercise improved the total GHQ scores, perceived competence/self-esteem, and coping as measured by the GHQ subscales. There were no significant effects of diet or exercise on quality of life, depression or anxiety. A high rate of participation in the exercise programme (>70%) was associated with greater improvements in total GHQ scores, anxiety, perceived competence/self-esteem and coping.