The aim of this research was to develop a brief scale of gay men's optimism-scepticism in the context of new HIV treatments. Following comprehensive literature search and communication with other researchers, 34 items about viral load testing, HIV therapies and concern about HIV infection were generated. By way of anonymous, self-complete questionnaires, these items were put to 532 gay men recruited at the Sydney Gay and Lesbian Mardi Gras Fair Day in February 1999. Principal axes factor analysis and item refinement yielded an optimism-scepticism scale based on 12 items (range 12-48, with higher scores indicating greater optimism). The sample mean was 19.8 (SD = 4.7). The scale had high internal consistency reliability (Cronbach's alpha = 0.79). Providing preliminary evidence of validity, men who reported unprotected anal intercourse with a causal partner 'in the past six months' had a significantly higher mean score (21.3) than those who did not report this risk practice (19.5, p < 0.001). Similar validation was provided from separate samples of gay men in Queensland and Sydney. Our scale of optimism-scepticism in the context of new HIV therapies is a brief, reliable instrument which can be incorporated within broader questionnaires and interview schedules. It is a useful tool to monitor attitudes toward HIV therapies and possible associations with risk practices.