The objective of this study is to describe functional profiles of patients with myasthenia gravis (MG), and the relationships among symptoms, activities and environmental factors (EF), by using WHO's International Classification of Functioning Disability and Health (ICF). Patients were consecutively enrolled at the Besta Institute of Milan, Italy. The ICF checklist was administered and two count-based indices were developed: "extension", containing ICF categories rated with qualifiers 1-4, and "severity", containing ICF categories rated with qualifiers 3-4. Spearman's correlation was performed to identify the relationships among symptoms, activities and EF, and linear regressions to identify the best predictors of performance indices in the activities and participation (A and P) domains. One hundred and one patients joined this study. Different values are reported in capacity and performance, the latter being 17.1% less limited in "extension" and 13% in "severity" index. Higher correlation indices are observed between A and P and body functions (BFs), than between A and P and EF. Problems in A and P are better explained by BF impairments than by facilitators within EF. In conclusion, EF plays a relevant role in improving MG patients' functioning. Nevertheless, difficulties in A and P, such as lifting objects or doing housework, are explained more by impairments in BF (e.g. in muscle endurance) than by the effect of EF (e.g. drugs and the support of family members). Methodologies and tools are needed to couple symptoms assessment with an evaluation of difficulties in executing activities and the environment's role, to plan appropriate interventions to meet MG patients' needs, especially in the labour sector, as 20% of patients gave up working before the retirement age.