During chemosensory evaluation, mice assess the health status of conspecifics. We hypothesize that health state detection is mediated via the accessory olfactory system. We address this hypothesis using an integrated approach. Combining chemical analysis of urine, physiological recordings of vomeronasal sensory neurons, and behavioral responses to chemosignals from healthy versus sick individuals, we investigate the neural basis of sickness detection in mice. Using animals, which develop a chronic colitis upon T-cell injection, we monitor disease progression and collect urine / bedding from individuals at defined time points. Our experiments reveal i) health state-dependent activation patterns of vomeronasal sensory neurons, ii) the molecular identity of candidate sickness-related cues, and iii) their effects on ecologically relevant social behaviors in group-housed animals. Together, we provide chemical, physiological, and behavioral evidence that supports a concept of sickness-related cue processing via the mouse accessory olfactory system.