BACKGROUND AND OBJECTIVES:In a pilot study, we previously demonstrated a higher average skin to lumbar epidural space distance (STLESD) in our obstetric population compared with the published literature. Furthermore, we demonstrated differences in STLESD based on ethnicity. The aim of this study was to perform a comprehensive analysis of the STLESD in our patient population by expanding the number of patients and ethnic groups included. METHODS:Data from 3,305 patients were obtained from our electronic database from September 2003 through November 2005. Self-declared ethnicity included 1,177 Caucasians (36%), 1,162 African Americans (35%), 760 Hispanics (23%), 135 Asians (4%), and 71 Indian/Pakistani/Bangladeshi/Sri Lankans (2%). The influences of body mass index (BMI), ethnicity, and their interaction on the STLESD were tested with a multiple linear regression model. RESULTS:The mean +/- SD STLESD differed among the ethnic groups ranging from 4.8 +/- 0.9 cm in Asian patients to 6.3 +/- 1.6 cm in African American parturients. When all ethnic groups were compared, BMI had a significant influence on STLESD (P < .0001), but so did ethnicity (P = .0004). The Hispanic group demonstrated STLESDs that were significantly lower than the African American and Caucasian groups at high BMI (P < .0001). In a subanalysis performed without the Hispanic group, the influence of BMI on STLESD was found to be similar for each group. In this subanalysis, the African American group had STLESDs that were deeper compared with the other 3 ethnic groups (P < .0001), regardless of BMI. CONCLUSIONS:In this study we found that the STLESD was deeper than what was previously reported in the literature. Furthermore, ethnicity, in addition to BMI, influenced the STLESD.