Preclinical studies suggest progesterone is neuroprotective after cerebral ischemia. The gold standard for assessing intervention effects across studies within and between subgroups is to use meta-analysis based on individual animal data (IAD). Preclinical studies of progesterone in experimental stroke were identified from searches of electronic databases and reference lists. Corresponding authors of papers of interest were contacted to obtain IAD and, if unavailable, summary data were obtained from the publication. Data are given as standardized mean differences (SMDs, continuous data) or odds ratios (binary data), with 95% confidence intervals (95% CIs). In an unadjusted analysis of IAD and summary data, progesterone reduced standardized lesion volume (SMD -0.766, 95% CI -1.173 to -0.358, P<0.001). Publication bias was apparent on visual inspection of a Begg's funnel plot on lesion volume and statistically using Egger's test (P=0.001). Using individual animal data alone, progesterone was associated with an increase in death in adjusted analysis (odds ratio 2.64, 95% CI 1.17 to 5.97, P=0.020). Although progesterone significantly reduced lesion volume, it also appeared to increase the incidence of death after experimental stroke, particularly in young ovariectomized female animals. Experimental studies must report the effect of interactions on death and on modifiers, such as age and sex.