This paper describes the psychometric properties of the Modern Homonegativity Scale (MHS), which measures contemporary negative attitudes toward gay men and lesbians (i.e., attitudes not based on traditional or moral objections to homosexuality). In Study 1 (N = 353), a preliminary version of the MHS was developed, and its psychometric properties were examined. Participants in Studies 2 and 3 (Ns = 308 and 233, respectively) completed the MHS and other attitudinal measures. The relationships among these variables were investigated to provide a more comprehensive assessment of the scale's construct validity. In Study 4 (N = 36), a behavioural expression of modern homonegativity was examined using the attributional ambiguity paradigm. The results of these studies indicate that the MHS is unidimensional, possesses a high degree of internal consistency, and is factorially distinct from a measure of old-fashioned homonegativity. As hypothesized, scores on the MHS correlated positively with political conservatism, religious behaviour, religious self-schema and modern sexism, but did not correlate significantly with social desirability bias. In addition, the MHS appears to be less susceptible to floor effects than a commonly used measure of old-fashioned homonegativity. Finally, the experimental study revealed that participants obtaining high scores on the MHS were less likely to sit beside individuals wearing T-shirts with pro-gay or pro-lesbian slogans when they could justify their seating choice on nonprejudicial grounds.