The objectives of this study were to investigate (1) the results of treatment with functional appliances in mixed dentition run by general practitioners, (2) factors associated with a final treatment result of overjet of > or = 5 mm and (3) the need of additional treatment with fixed appliances. The study was designed as a retrospective, cross sectional survey and conducted in one of the Public Dental Clinics and the Orthodontic Clinic in Lidköping, Sweden. 122 patients (aged 7.6 -13.2 years) with an overjet of > or = 7 mm and consecutively collected for treatment with functional appliance therapy. Patient files were analysed with regard to gender, age, initial class II severity, type of functional appliance, co-operation, overall growth, number of missed appointments and treatment time. The treatment results were studied and correlated with the above-mentioned variables. The need for additional treatment with fixed appliances was evaluated. A final overjet of < or = 5 mm was observed in 61.5% of the patients, 48.4% interrupted treatment prematurely and 33.6% received additional treatment with fixed appliances. Good co-operation and extended treatment time was found to be correlated with a final overjet of < or = 5 mm. Other factors not associated with treatment outcome were age, gender, overjet, overbite, molar relation, type of functional appliance, overall growth and number of missed appointments. Activator treatment was successful in reducing overjet to 5 mm or less in almost two thirds of the treated patients. Mainly because of poor functional appliance treatment results or relapse, one third of the patients were retreated with fixed appliance. Since good co-operation is one of the main factors for successful treatment outcome, evaluation of the motivational level of both the parents and the patient before treatment start is crucial.