Human immunodeficiency virus (HIV) and sexually transmitted infections (STI) testing rates are amongst the highest in the world among men who have sex with men (MSM) in Australia. However, notable minorities have never tested and many MSM have not tested recently. To examine testing routines and assess covariates of testing, an online survey was conducted among MSM in New South Wales. Five hundred and eighty non-HIV positive MSM (Mean age: 29.33 years) were randomized to answer questions on barriers to testing for HIV or STI. One in five (20.9 %) non-HIV-positive participants had never tested for HIV, 27.2 % had no HIV testing routines, 22.8 % had a moderate HIV testing routines, and 29.1 % had strong HIV testing routines. Similar patterning was observed for STI testing. In multivariate analyses participants’ knowledge, beliefs, attitudes, subjective norms and perceived behavioral control were moderately related to HIV and/or STI testing routines and some associations were specific to either HIV or STI testing or to particular routines. Findings highlight that multiple social-cognitive factors each play a role in explaining HIV and STI testing among MSM. To effectively promote regular testing in MSM, programs face the challenge of having to address a range of hurdles, rather than a few major obstacles.