Objective: To examine the epidemiology and severity of self-poisoning by older people in Australia; to compare these data with those for overdoses in younger adults. Design, setting, participants: A cohort study of people presenting to a tertiary toxicology centre after self-poisoning over 26 years (1987–2012). Main outcome measures: Hospital length of stay (LOS); types of drug ingested; intensive care unit (ICU) admissions; in-hospital deaths. Results: Of 17 276 admissions, 626 patients (3.6%) were at least 65 years old. There was a steady decline in the number of overdoses with age. Most self-poisoning by older people was intentional (80% of admissions), but the proportion of unintentional poisonings increased with age (P < 0.001). Median LOS for older patients was 34 h (interquartile range [IQR], 16–75 h), longer than for younger patients (16 h; IQR, 9–25 h; P < 0.001). 133 older patients (21.2%) were admitted to an ICU, compared with 1976 younger patients (11.9%; P < 0.001). 24 older patients (3.8%) and 93 younger patients (0.6%) died; mortality among older patients declined over time. Hypotension and arrhythmias were more common in patients over 65. Benzodiazepines (24%) were the drugs most commonly ingested by older patients, but opioids the most frequently taken drugs in fatal cases. Toxic ingestion of cardiovascular drugs increased threefold over the 26 years; about one-third of poisonings were unintentional or iatrogenic. Recreational drugs were implicated in the admissions of four older patients (0.6%), but in 7.8% of those of people under 65. Conclusion: Older patients treated for self-poisoning differ in several important respects from patients under 65. They are more severely affected by self-poisoning: LOS is greater, and ICU admission and mortality rates are higher.