CONTEXT: Swaddling is a traditional practice of wrapping infants to promote calming and sleep. Although the benefits and risks of swaddling in general have been studied, the practice in relation to sudden infant death syndrome remains unclear. OBJECTIVE: The goal of this study was to conduct an individual-level meta-analysis of sudden infant death syndrome risk for infants swaddled for sleep. DATA SOURCES: Additional data on sleeping position and age were provided by authors of included studies. STUDY SELECTION: Observational studies that measured swaddling for the last or reference sleep were included. DATA EXTRACTION: Of 283 articles screened, 4 studies met the inclusion criteria. RESULTS: There was significant heterogeneity among studies (I2 = 65.5%; P = .03), and a random effects model was therefore used for analysis. The overall age-adjusted pooled odds ratio (OR) for swaddling in all 4 studies was 1.58 (95% confidence interval [CI], 0.97-2.58). Removing the most recent study conducted in the United Kingdom reduced the heterogeneity (I2 = 28.2%; P = .25) and provided a pooled OR (using a fixed effects model) of 1.38 (95% CI, 1.05-1.80). Swaddling risk varied according to position placed for sleep; the risk was highest for prone sleeping (OR, 12.99 [95% CI, 4.14-40.77]), followed by side sleeping (OR, 3.16 [95% CI, 2.08-4.81]) and supine sleeping (OR, 1.93 [95% CI, 1.27-2.93]). Limited evidence suggested swaddling risk increased with infant age and was associated with a twofold risk for infants aged >6 months. LIMITATIONS: Heterogeneity among the few studies available, imprecise definitions of swaddling, and difficulties controlling for further known risks make interpretation difficult. CONCLUSIONS: Current advice to avoid front or side positions for sleep especially applies to infants who are swaddled. Consideration should be given to an age after which swaddling should be discouraged.