BACKGROUND: The association between the R allele of PON1 Q192R and symptoms reported by sheep dippers and Gulf War veterans has been used to suggest a biological basis for these symptoms. In the absence of such studies in non-occupational populations, these conclusions may not be valid. OBJECTIVE: To examine the association of paraoxonase (PON1) Q192R with a report of ever being diagnosed with depression among a random sample of 3266 British women, aged 60-79 years. RESULTS: The R allele of PON1 Q192R was associated with depression: per-allele odds ratio 1.22 (95% confidence interval: 1.05 to 1.41) in this population. CONCLUSIONS: These findings suggest that the association of PON1 Q192R with symptoms of depression in occupationally exposed groups may be driven by exposure to toxins that everyone in the general population is exposed to rather than exposure to toxins specifically used by sheep dippers or Gulf War veterans, or that other mechanisms underlie the association. This is because the study population in which we have found an association consisted of British women aged 60-79 years, few of whom were sheep dippers or Gulf War veterans. When using genotype-outcome associations to infer causality with respect to an environmental exposure modified by the genotype, it is important to examine these associations in general populations and in those specifically exposed to the putative agent. The possible role of PON1 Q192R in psychiatric morbidity requires further examination.