Acculturation has become a popular variable in research on health disparities among certain ethnic minorities, in the absence of serious reflection about its central concepts and assumptions. Key constructs such as what constitutes a culture, which traits pertain to the ethnic versus "mainstream" culture, and what cultural adaptation entails have not been carefully defined. Using examples from a systematic review of recent articles, this paper critically reviews the development and application of the concept of acculturation in US health research on Hispanics. Multiple misconceptions and errors in the central assumptions underlying the concept of acculturation are examined, and it is concluded that acculturation as a variable in health research may be based more on ethnic stereotyping than on objective representations of cultural difference.