This study aimed to explore the characteristics and range of gastrointestinal (GI) motility problems in adult patients with mitochondrial disease. We retrospectively identified 30 patients with molecularly and/or biopsy-proven mitochondrial disease who during the course of their clinical work-up, had formal gastric and colonic transit studies. We reviewed their upper and lower GI symptoms over time, and compared these with their GI transit studies, nutrition level, diabetic status, and their response to various management options. Of the 30 patients, 12 had the m.3243 A>G mutation (six had mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes); three had other mitochondrial point mutations; two had polymerase gamma (POLG) mutations; two had mitochondrial neurogastrointestinal encephalopathy, five had chronic progressive external ophthalmoplegia, and six had multi-systemic manifestations. Upper and lower gastrointestinal segments were variably involved. Increasing fibre intake or stool softener was less effective than osmotic or stimulant laxatives, and bowel rest in severe cases. Fluctuation in GI motility may relate to exacerbations in other organ systems. Patients' average body mass indices were low average, and caloric, vitamin and iron deficiencies may necessitate parenteral replacement. GI dysmotility is a common problem amongst patients with a range of mitochondrial conditions, with involvement of different segments of the gastrointestinal tract. Gastrointestinal dysmotility should be screened regularly in patients with suspected mitochondrial disease. Acute exacerbation of gastrointestinal dysmotility may relate to a generalised deterioration. Both oral and parenteral administration of caloric, vitamin and iron supplementation should be considered when these nutritional deficiencies are present.