Quantifying the demography of wildlife populations is imperative to evaluating population trends, but identifying mechanisms that influence demographic outcomes can be difficult for cryptic species. We radio-tracked Pacific martens (Martes caurina), an elusive mesocarnivore, to estimate survival, determine causes of mortality, and assess co-occurring pathological conditions. We tracked 18 female and 33 male martens for an average (±SD, range) of 16.35 months (±8.7, 1–41) from 2009–2013 and 2015–2017 in northern California. Annual survival rates were 0.81 (95% CI = 0.66–0.95) and 0.68 (95% CI = 0.57–0.79) for female and male martens, respectively. We documented 16 marten mortalities, 13 of which were suspected predation events. Seven mortalities were confirmed as predations via clinical forensic evidence, with bobcats (Lynx rufus; n = 5) representing all clinically confirmed predations. The proximate cause of mortality for one marten was attributed to toxicosis from anticoagulant rodenticide exposure, which has not been previously reported in free-ranging martens. Further, martens appeared to be more vulnerable to predation during reproductive periods that incur increased energetic requirements (e.g., lactation, kit-rearing, mating). We propose continued pairing of field and clinical assessments to better substantiate causes of mortality, elucidate pathology, and identify novel stressors.