The objective of this study was to examine factors associated with self-reporting of chronic health problems. The self-reports were obtained from a questionnaire sent by mail to the French GAZEL cohort, composed of workers of a French company. The disorders reported in the questionnaire were compared with diagnoses from the sick-leave database of the company. Associations between self-reporting and characteristics were studied by multiple logistic regression analyses. Three types of characteristics were analyzed: individual, methodological and disorder-related (i.e., prevalence of chronic disorders in the general population, probable disability and probable life risk scores). In 1992, the cohort consisted of 16,534 subjects aged 38 to 53 years. The reporting rate (number of self-reports in the questionnaire divided by number of records in the sick-leave database for the disorder considered) varied from 8.9% to 100%. Self-reporting was associated with individual characteristics (gender, family status, place of residence, annual number of sick days and sick leaves), disorder-related characteristics (probable disability, prevalence) and methodological characteristics (precision of the formulation, delay between the last sick-day and the patient report). By body system, the characteristics associated with self-reporting varied greatly but the annual number of sick days, probable disability and precision of formulation were the variables which remained most often in the models. These characteristics should be particularly taken into consideration in the interpretation of epidemiological results based on self-reporting.