Auditory Hallucinations (AH) cause substantial suffering and dysfunction, yet remain poorly understood and modeled. Previous reports have linked AH to increases in negative emotions, suggesting a role for the autonomic nervous system (ANS) in underlying this link. Employing an Experience Sampling Method (ESM) approach, 40 individuals with schizophrenia completed a 36-hour ambulatory assessment of AH and cardiac autonomic regulation. Participants carried mobile electronic devices that prompted them to report 10 times/d the severity of their momentary AH, along with a Holter monitor that continuously recorded their cardiac autonomic regulation. The clocks of the devices and monitors were synchronized, allowing for high time-resolution temporal linking of the AH and concurrent autonomic data. Power spectral analysis was used to determine the relative vagal (parasympathetic) contribution to autonomic regulation during 5 minutes prior to each experience sample. The participants also completed interview-based measures of AH (SAPS; PSYRATS). The ESM-measured severity of AH was significantly correlated with the overall SAPS-indexed AH severity, along with the PSYRATS-indexed AH frequency, duration, loudness, degree of negative content, and associated distress. A mixed-effect regression model indicated that momentary increases in autonomic arousal, characterized by decreases in vagal input, significantly predicted increases in ESM-measured AH severity. Vagal input averaged over the 36-hour assessment displayed a small but significant inverse correlation with the SAPS-indexed AH. The results provide preliminary support for a link between ANS regulation and AH. The findings also underscore the highly dynamic nature of AH and the need to utilize high time-resolution methodologies to investigate AH.