BACKGROUND: Exposure to a complex emergency has a substantial psychological component, which is rarely assessed. This study compares the health impact of physically and psychologically mediated exposure to a complex emergency. SETTING: The Sea Empress oil tanker spill. DESIGN: A cross-sectional analysis of self-report questionnaire responses collected from inhabitants of 6 different coastal towns-4 of them physically exposed to the oil spill, 2 unexposed-was undertaken. The towns were known to be psychologically homogeneous before the incident. Perceived risk was used as a measure of psychological exposure. Anxiety, depression and symptom reporting were used as measures of health impact. PARTICIPANTS: 1089 (69%) men and women aged 18-65 years responded. MAIN RESULTS: Perceived risk was associated with raised anxiety and non-toxicologically related symptom reporting, whereas physical exposure to oil was only associated with toxicologically related symptom reporting. The impact of raised perceived risk on the population was greater than that of physical oil exposure, involving more persons over a wider area. CONCLUSIONS: Psychological exposure was shown to be quantifiable, and to be a substantially more sensitive measure of health impact than physical exposure in relation to psychological outcomes. This type of analysis has important implications for emergency response planning, and for the interpretation of a complex emergency by the general public.