Background Peroxisome proliferator-activated receptor gamma (PPAR-gamma) agonists are insulin-sensitising drugs used for the treatment of insulin resistance. In addition to lowering glucose in diabetes, these drugs may also protect against hyperlipidaemia and arteriosclerosis, which are risk factors for stroke. Objectives To assess the efficacy and safety of PPAR-gamma agonists in the secondary prevention of stroke and related vascular events for people with stroke or transient ischaemic attack (TIA). Search methods We searched the Cochrane Stroke Group Trials Register (July 2015), the Cochrane Central Register of Controlled Trials (CENTRAL 2015, Issue 6), MEDLINE (1949 to July 2015), EMBASE (1980 to July 2015), CINAHL (1982 to July 2015), AMED (1985 to July 2015) and 11 Chinese databases (July 2015). In an effort to identify further published, unpublished and ongoing trials we searched ongoing trials registers, reference lists and relevant conference proceedings, and contacted authors and pharmaceutical companies. We did not impose any language restrictions. Selection criteria We included randomised controlled trials (RCTs) evaluating PPAR-gamma agonists versus placebo for the secondary prevention of stroke and related vascular events in people with stroke or TIA, with the outcomes of recurrent stroke, vascular events and adverse events. Data collection and analysis Two review authors independently screened the titles and abstracts of identified records, selected studies for inclusion, extracted eligible data, cross-checked the data for accuracy, and assessed methodological quality and risk of bias. Main results We identified four eligible studies with 1163 participants; only one study had a low risk of bias for all domains. Three studies evaluated the drug pioglitazone and one study evaluated rosiglitazone. The participants in different studies were heterogeneous. The number of participants with recurrent stroke was evaluated in two studies, where PPAR-gamma agonists reduced the recurrence of stroke compared with placebo (risk ratio (RR) 0.52, 95% confidence interval (CI) 0.34 to 0.80). PPAR-gamma agonists given over a mean duration of 34.5 months in a single trial were found to reduce a composite outcome of total events of cardiovascular death, non-fatal myocardial infarction or non-fatal stroke (RR 0.73, 95% CI 0.54 to 0.99). Data on additional composite outcomes reflecting serious adverse events (all-cause death and other major vascular events; all-cause mortality, non-fatal myocardial infarction or non-fatal stroke) were similar although the confidence intervals were wider and the effects were not statistically significant. In addition, two studies respectively measured insulin sensitivity and the ubiquitin-proteasome activity in carotid plaques. These results were significantly improved by PPAR-gamma agonists in comparison with placebo. None of the studies reported the number of participants with disability due to vascular events or improvement in quality of life. Three RCTs reported information about adverse events. Frequent adverse events included oedema, cardiac failure and anaemia. Evidence that adverse events occurred more frequently in participants treated with PPAR-gamma agonists when compared with placebo was imprecise and inconsistent (risk difference (RD) 10%, 95% CI -8% to 28%, I-2 = 86%). Authors' conclusions PPAR-gamma agonists appear to reduce recurrent stroke and total events of cardiovascular death, non-fatal myocardial infarction or non-fatal stroke, and improve insulin sensitivity and the stabilisation of carotid plaques. There is evidence of limited quality that they are well tolerated. However, the conclusions should be interpreted with caution considering the small number and the quality of the included studies. In future, well-designed, double-blind RCTs with large samples are required to assess the efficacy and safety of PPAR-gamma agonists in the secondary prevention of stroke and related vascular events in people with stroke or TIA.