Background: Pioglitazone is an antidiabetic drug that belongs to the thiazolidinedione (TZD) class of insulin-sensitizing agents. Adverse events to pioglitazone of potential severity are listed in the `special warnings and special precautions for use' section of the pioglitazone summary of product characteristics (SPC), with recommendations for monitoring and management. Objective: To describe the risk management and outcomes of recognized TZD class effects in patients prescribed pioglitazone. Methods: An observational study of risk management and event outcomes for the adverse events of cardiac failure, fluid retention/oedema, weight gain, anaemia and abnormal liver function tests (LFTs) was performed. Patients were identified from within a prescription-event monitoring (PEM) postmarketing cohort of first-users of pioglitazone. Patients with pre-existing events or alternative causes, or with no possibility of collecting further information, were excluded. Outcomes included (i) the method of detection of the adverse event, i.e. whether the patient or the prescriber identified the problem; (ii) whether responsibility for risk management was taken at a primary- or secondary-care level; (iii) interventions taken to manage the event, including discontinuation of treatment; (iv) resolution and/or other outcomes of the event; and (v) general practitioner (GP) opinion of relatedness of the event to pioglitazone. Results: Acute events such as cardiac failure and oedema were more likely to be detected by the patient presenting with the event rather than at regular follow-up. GPs were more likely to take responsibility for management of abnormal LFTs, anaemia and oedema events, whereas hospital admissions occurred mainly in patients with cardiac failure (45.3%). Pioglitazone was stopped in more than 50% of each type of event, apart from anaemia. Oedema events were the most likely to resolve (87.6%) and anaemia the least likely (42.9%). Oedema events were the most likely to be attributed to the drug by GPs, whereas cardiac failure was the event least attributed to pioglitazone. Conclusions: Timely drug withdrawal and/or interventions such as corrective treatment or referral to a specialist can lead to successful resolution of class-effect adverse events of pioglitazone. Regular follow-up of patients on antidiabetic agents is essential to detect certain events, but more acute events are more likely to be reported spontaneously. Treatment options for patients with diabetes mellitus and cardiovascular risk factors are limited, requiring careful benefit-risk assessment of pioglitazone use in these patients and careful monitoring for signs of worsening cardiac function.