The purpose of the study was to describe the illness behavior and assimilation of first and second generation Lebanese Americans and to explore the relationship between assimilation and illness behavior among the study group. Illness behavior was defined as symptom perception, symptom evaluation, and action taken in response to perception and evaluation. Assimilation was defined as a function of acculturation, social identification, social integration and amalgamation. A convenience sample of 82 subjects was obtained through snowballing technique. The participants responded to oral administration of the Cornell Medical Index Revised (Miskovitz, 1986), Koos' List of Symptoms (Koos, 1954), the Language Acculturation Scale (Deyo, Diehl, Hazuda, & Stern, 1985), and a questionnaire designed to elicit beliefs and a cultural conceptualization related to illness behavior (based on Kleinman) and assimilation of Lebanese Americans (based on Yinger). Qualitative and quantitative methods were used for data analysis. The investigation demonstrated statistically significant differences between first and second generation Lebanese Americans in terms of psychological symptom perception and the four assimilation subprocesses. Significant relationships were also identified among some of the sociodemographic variables, symptom perception, perception of symptom seriousness and the four assimilation variables. An inverse statistically significant relationship was found between perception of psychological symptoms and three of the assimilation variables: acculturation, social identification and amalgamation. An inverse statistically significant relationship between symptom perception variables and perception of seriousness of symptoms was identified. The results also demonstrated that health and illness beliefs and behavior of first generation Lebanese Americans integrated traditional and western beliefs and practices. Second generation Lebanese Americans were mostly influenced by the western beliefs and practices. Conclusions pointed to the need of understanding cultural beliefs and practices and their influence on health and illness behavior, but also identified the need to assess for cultural diversity to mitigate overgeneralization and stereotyping of all members of an ethnic group. Implications of this study for nursing knowledge and practice and recommendations for further research are discussed.