Theory predicts that cheating individuals should alter their behaviour to avoid detection, yet empirical data for such 'deceptive' behaviour (and its putative consequence-punishment) is almost entirely absent from the literature. This dearth of evidence, particularly among primates, limits our understanding of the evolution of deception and punishment. Here, we quantify deception and punishment in a reproductive context in wild geladas (Theropithecus gelada). Individuals involved in extra-pair copulations (9% of observed copulations) exhibited behaviour consistent with tactical deception: they were less likely to vocalize and more likely to copulate when the cuckolded male was a sizable distance away (>20 m). Further, many extra-pair copulations (∼20%) elicited post-copulatory aggression-likely, punishment-from cuckolded males. This rare empirical evidence of both tactical concealment and retaliatory aggression offers a potential model system for examining the co-occurrence of deception and punishment in natural settings.