This chapter reviews the differences in the aetiology of gastrointestinal symptoms, adverse drug reactions and efficacy of treatment for functional gastrointestinal disorders (FGIDs) in elderly cohorts. Medications can frequently be the source of gastrointestinal symptoms mistaken for an FGID. Medications used to treat FGIDs can cause side effects or drug-drug interactions with other prescribed or over-the-counter agents. Comorbid physical and mental illness can have a significant impact on the aetiology, presentation and treatment of gastrointestinal syndromes. Most malignancies, particularly gastrointestinal cancers, increase in incidence with advancing age and frequently present with symptoms overlapping those of FGIDs. The elderly are more susceptible to medication side effects. Age-related changes affecting drug pharmacokinetics and pharmacodynamics include reductions in lean muscle mass and water content, increased body fat, decreased albumin, reduced liver mass and perfusion, and decreased glomerular filtration rates. Medications and other non-malignant diseases should also be considered and excluded as the source of symptoms before concluding that an FGID exists.