OBJECTIVE To identify factors associated with dehiscence and mortality rates following gastrointestinal surgery in dogs. ANIMALS 170 client-owned dogs that underwent gastrointestinal surgery from 2010 to 2016. PROCEDURES Medical records of all included dogs were reviewed to collect information on preoperative (breed, sex, age, body weight, American Society of Anesthesiologists [ASA] physical status classification, emergency status, and plasma lactate concentration), intraoperative (indication for surgery, type of surgery, and whether bacterial peritonitis was identified), and postoperative (development of dehiscence and survival status at 2 weeks after surgery) factors. Preoperative and intraoperative factors were evaluated for associations among each other and with postoperative factors. RESULTS Univariate analyses revealed that preoperative plasma lactate concentration increased with increasing ASA status, and lactate concentrations were significantly higher for nonsurvivors (mean ± SD, 4.6 ± 3.7 mmol/L) than for survivors (2.4 ± 1.7 mmol/L). Multivariate analysis controlling for age, body weight, and plasma lactate concentration revealed that dogs with an ASA status ≥ 3 were more likely to develop dehiscence after gastrointestinal surgery than were dogs with a lower ASA status (OR, 17.77; 95% confidence interval, 2.17 to 144.06). Multivariate analysis also revealed that dogs with an ASA status ≥ 3 or high lactate concentration were less likely to survive than were other dogs. CONCLUSIONS AND CLINICAL RELEVANCE These findings regarding ASA status and preoperative plasma lactate concentration and their associations with outcome may help clinicians to determine and provide optimal perioperative care to dogs requiring gastrointestinal surgery as well as to inform owners about prognosis.