PURPOSE: In-patients characteristics generate cost differences between hospitals. In France, there are few data on the characteristics on the patients referred to hospitals by their general practitioners (GPs) and none on the predictors of referral to the public or for-profit hospitals. The aim of this study was to analyze those characteristics and the predictors of referral to the public or for-profit hospitals. METHODS: We collected, prospectively, the request for hospitalizations made by the GPs of the Sentinelles network in France, from 2007 to 2009. Patients' characteristics and also the reasons for that request were analyzed. A logistic regression was used to compare the population between local hospitals. RESULTS: Ten thousand seven hundred and eighteen statements were collected. The median age was 73 years. Patients were women in 51% of the cases, and only 14% of the hospitalizations had been planned. Hospitalization in the public sector was preferred for young children and the elderly (P<0.001). When compared to the patients referred to the private sector, patients addressed to the public sector were more often seen for emergencies (OR: 2.3 [2.0-2.8]), by a doctor different from their referring GP (OR: 1.7 [1.4-2.1]) and out of the GP's office. The reasons for hospital admission were different depending on the sector of hospitalization (P<0.001), patients addressed to the public sector hospitals presented with greater comorbidity or more complex diagnosis (for example: feeling ill, fainting or syncope and fever) or a greater disability (for example: stroke, neurological and psychiatric diseases). CONCLUSION: This study suggests that GPs send their patients to the public or for-profit hospitals according to criteria of severity, comorbidity and disability.