Social influences may create a barrier to couples HIV testing and counselling (CHTC) uptake in sub-Saharan Africa. This secondary analysis of data collected in the 'Uthando Lwethu' randomised controlled trial used discrete-time survival models to evaluate the association between within-couple average 'peer support' score and uptake of CHTC by the end of nine months' follow-up. Peer support was conceptualised by self-rated strength of agreement with two statements describing friendships outside of the primary partnership. Eighty-eight couples (26.9%) took up CHTC. Results tended towards a dichotomous trend in models adjusted only for trial arm, with uptake significantly less likely amongst couples in the higher of four peer support score categories (OR 0.34, 95% CI 0.18, 0.68 [7-10 points]; OR 0.53, 95% CI 0.28, 0.99 [>/= 11 points]). A similar trend remained in the final multivariable model, but was no longer significant (AOR 0.59, 95% CI 0.25, 1.42 [7-10 points]; AOR 0.88, 95% CI 0.36, 2.10 [>/= 11 points]). Accounting for social influences in the design of couples-focused interventions may increase their success.