Previous studies on individual foods and nutrients and Parkinson's disease (PD) risk have been inconsistent. Furthermore, only one study has examined the association between the quality of diet and PD. We investigated the prediction of food groups and diet quality on PD in the Finnish Mobile Clinic Survey (1966–72). The population comprised 4524 individuals, aged 40–79 years and free from PD at baseline. Data collection included health examinations, a questionnaire and a 1-year dietary history interview. A modified Alternate Healthy Eating Index was formed to assess diet quality. Statistical analyses were based on Cox's model. During a 41-year follow-up, eighty-five incident cases of PD occurred. No statistically significant associations were found between PD incidence and most of the food groups examined. A few exceptions were fruits and berries in men and milk in women, which showed positive associations. An inverse association between the intake of meat products and PD was found in women. The diet quality index did not predict PD, the adjusted relative risk between the highest and lowest quartiles being 1·83 (95 % CI 0·65, 5·18) in men and 0·97 (95 % CI 0·38, 2·48) in women. The present study suggests that since most of the single food groups or the quality of diet did not predict PD occurrence, the role of diet is apparently rather modest.