BACKGROUND: Constipation is suspected to occur frequently after acquired brain injury (ABI). In patients with ABI, heart rate variability (HRV) is reduced suggesting autonomic dysfunction. Autonomic dysfunction may be associated with prolonged gastrointestinal transit time (GITT). The primary aim of this study was to investigate if GITT is prolonged in patients with ABI. Secondarily, HRV and its correlation with GITT was investigated. METHODS: We included 25 patients with ABI (18 men, median age: 61.3 years, range [30.7-74.5]). GITT was assessed using radio-opaque markers and HRV was calculated from 24-hour electrocardiograms. Medical records were reviewed for important covariates, including primary diagnosis, time since injury, functional independence measure, and use of medication. The GITT assessed in patients was compared to a control group of 25 healthy subjects (18 men, median age: 61.5 years, range [34.0-70.9]). RESULTS: In ABI patients, the mean GITT was significantly longer than in healthy controls (2.68 days, 95% CI [2.16-3.19] versus (1.92 days, 95% CI [1.62-2.22], p = 0.011)). No correlation was found between HRV and GITT. CONCLUSION: Patients with mild to moderate ABI have prolonged GITT unrelated to the HRV.