We examined HIV optimism and unprotected anal intercourse (UAI) in a nationwide sample of gay and homosexually active men. Questionnaires were distributed throughout Australia through pornographic catalogues. 1832 men responded, 1181 (64.5%) classified as gay community attached (GCA) and 651 (35.5%) as non-GCA (NGCA). Mean HIV optimism scores tended toward scepticism rather than optimism, with no significant difference between GCA and NGCA men. Men who had UAI with regular partners were significantly more optimistic than men who did not (P<0.001). There was a significant UAI-casual/GCA interaction (P<0.001). GCA men who engaged in UAI-casual were significantly more optimistic than GCA men who did not (P<0.001). Likewise, NGCA men who had UAI-casual were significantly more optimistic than NGCA men who did not (P<0.001). These findings corroborate earlier evidence that gay men's UAI is associated with - not necessarily caused by - HIV optimism. Importantly, these data come from a broad national sample rather than one drawn from within a 'gay precinct'.