Such widespread functional gastrointestinal disorders as irritable bowel syndrome (IBS) and functional dyspepsia (FD), although not represented by any obvious structural lesions of the gastrointestinal tract, but they seriously affect quality of life of many patients. According to epidemiological data, 26.7 — 48.7 % of IBS patients and 20.0 — 42.1 % of patients with FD have a crossover of symptoms, also known as overlap IBS/FD syndrome. Overlap syndrome usually leads to more serious clinical manifestations, deterioration of quality of life and complications. Chronic low‑intensity post‑infectious inflammation or non‑infectious microinflammation and the immune response play an important role in the pathogenesis of both IBS and FD, leading to visceral hypersensitivity, dysfunction of «brain‑gut» axis and intestinal mucosal barrier, which are usually the cause of IBS or FD. However, whether inflammation has the same mechanism in the syndrome of the overlap of IBS and FD (IBS/FD) remains unclear. The presented review considers the latest advances in the study of inflammatory mechanisms in IBS/FD and proposes new treatment tactics. Current data on the role of gastrointestinal infection, secondary chronic inflammation and immune response, intestinal mucosal barrier damage associated with gastrointestinal infection, effects of gastrointestinal infections on the enteric nervous system and the «gut‑brain» axis, possible role of Helicobacter pylori infection at the overlap of IBS/FD are discussed. The role of non‑infectious inflammation, in particular, bacterial overgrowth syndrome, food allergy, psychological or mental stress in the pathogenesis of IBS, FD and IBS/FD overlapping is also considered. The modern tactics of treatment and management of such patients, which is based on the impact on inflammatory mechanisms also are presented.