Over one third of patients with myotonic muscular dystrophy type 1 (DM1) have gastrointestinal complaints. The cause is multifactorial, and treatment options are limited. Twenty DM1 patients with gastrointestinal symptoms were screened over a 2-year period using glucose breath hydrogen testing (GBHT) to evaluate the prevalence of small intestinal bacterial overgrowth (SIBO). Sixty-five percent of patients had a positive GBHT, and diarrhea was the most common presenting symptom. Ciprofloxacin was the most common antibiotic used for treatment, and 70% of patients reported a good response to the initial course of treatment. Although the causes of gastrointestinal symptoms in patients with DM1 are multifactorial, small intestinal bacterial overgrowth is an important diagnostic consideration that is easily diagnosed using glucose breath hydrogen testing and often shows a good response to treatment with common antibiotics.