Strongylus vulgaris is regarded the most pathogenic helminth parasite infecting horses. It was once estimated to be the primary cause of colic in horses and has been termed the horse killer. Disease is ascribed to thromboembolism caused by larvae migrating in the mesenteric arteries eventually leading to ischemia and infarction of intestinal segments. This causes a painful colic with an often fatal outcome. However, this knowledge is derived from studies with experimental inoculation of parasite-naïve foals and case studies. This documents the pathogenic potential of the parasite, but does not address its role as risk factor for colic in horse populations. This study was designed as a retrospective case-control study among equine patients referred to the University of Copenhagen Large Animal Hospital during 2009-2011. Every referred colic case was matched with a patient of the same type (pony, warmblooded, coldblooded), age, gender, and admitted in the same month and year, but for problems unrelated to the gastrointestinal tract. Serum samples were analyzed for antibodies to migrating S. vulgaris larvae using a recently developed ELISA. Three case definitions were used; colic sensu latum (n=274), idiopathic colics (n=48), and strangulating (n=55) vs. nonstrangulating infarctions (n=22). Odds ratios (OR) revealed no statistical association with ELISA results for the colic sensu latum and idiopathic colic case definitions. However, nonstrangulating infarctions were strongly associated with higher S. vulgaris titers, when compared to strangulating infarctions (OR=4.12, P=0.01). Colic is a very broadly defined symptom complex with numerous possible risk factors unaccounted for. Horses can harbor S. vulgaris infection without showing clinical symptoms, and a recent study illustrated that a positive ELISA result should be interpreted as exposure to the parasite within the preceding five months. Nonetheless, the ELISA may be helpful in evaluating the more severe colic categories involving infarctions in the abdominal cavity.