Longer-term immigrants residing in the United States exhibit physical health decline related to higher body mass index (BMI). Theories on immigrant acculturation have been used to examine health patterns by length of stay in the United States. The purpose of this cross-sectional study, guided by the Schwartz model of acculturation, was to examine the effect of acculturation and length of stay in the United States on BMI in a sample of Haitian immigrants living in the Northeast Metropolitan area. The research question was used to examine the effects of acculturation and length of stay on BMI in the convenience sample of 116 Haitian men and women, aged 18 years and older, who had relocated to the United States for 3 years or more. Data were collected using a demographic questionnaire and medical records from a participating health clinic and then analyzed by conducting a multiple linear regression. According to study results, acculturation, length of stay, age, gender, and physical activity were not significant predictors of BMI change. An ancillary analysis using the subscales of acculturation revealed similar results. This study may provide positive social change by enabling health providers to understand the beliefs, values, and practices of Haitian immigrant groups and the acculturation pattern of individuals when providing care for this population.