The purpose of this study was to evaluate the relationship between head trauma and Parkinson's disease (PD). A questionnaire was completed by 97 PD patients (mean age 68.6 years, duration of disease 6.4 years) and 64 spouses acting as controls (mean age 63 years). Thirty-one PD patients reported head trauma before onset of PD (mean 32.3 years earlier), whereas 11 controls reported head injury before completing the survey (mean 26 years earlier) (p less than 0.05). Twenty PD patients and five controls reported head injury associated with alteration or loss of consciousness (p less than 0.05). Injury occurred a mean of 37.7 years before onset of PD and 37.2 years before survey completion in the two groups, respectively. In both of these comparisons we adjusted the frequencies to eliminate sex differences between groups. Comparison of new frequencies showed differences that were not significant. However, a trend toward significance was observed when examining head trauma with alteration of consciousness. Other investigators have reported similar results indicating that previous head trauma may be a risk factor in the etiology of PD. However, recall bias might have an effect on the outcome of these studies and this is discussed. The relationship between head trauma and PD is still tenuous.