[영문]Objectives: In 1994, the US Public Health Service launched the qqqquot;Back to Sleepqqqquot; campaign, promoting the supine sleep position to prevent sudden infant death syndrome (SIDS). Studies of SIDS in the United States have generally found socioeconomic and race disparities. Our objective was to see whether the qqqquot;Back to Sleepqqqquot; campaign, which involves an effective, easy, and free intervention, has reduced social class inequalities in SIDS. Methods: We conducted a population-based case-cohort study during 2 periods, 1989 to 1991 and 1996 to 1998, using the US Linked Birth/Infant Death Data Sets. Case group was infants who died of SIDS in infancy (N = 21 126); control group was a 10% random sample of infants who lived through the first year and all infants who died of other causes (N=2241218). Social class was measured by mother’s education level. Results: There was no evidence that inequalities in SIDS were reduced after the Back to Sleep campaign. In fact, odds ratios for SIDS associated with lower social class increased between 1989?1991 and 1996?1998. The race disparity in SIDS increased after the Back to Sleep campaign. Conclusions: The introduction of an inexpensive, easy, public health intervention has not reduced social inequalities in SIDS; in fact, the gap has widened. Although the risk of SIDS has been reduced for all social class groups, women who are more educated have experienced the greatest decline