BACKGROUND AND OBJECTIVE: Compliance with weight reducing programs can be improved by intensive care and control. We tested a telemetrically-guided weight reduction program in overweight and obese persons. PATIENTS AND METHODS: 200 outpatients (62 males) with a mean body mass index of 34 kg/m 2 and a mean age of 47 years participated in a prospective study for one year. During the first six months, telemetrical support (weight-transmission via Bluetooth (short range)-technology, 20-minutes telephone consultation with a nutritionist) was given weekly. After six months, participants were randomly assigned either to a group with further telemonitoring support (telemetric group) or to a group without contact to our clinic (control group). At baseline, and after six and twelve months, body weight, body composition (bioelectrical impedance analysis), and parameters of the metabolic syndrome were assessed at our clinic. RESULTS: 16 participants terminated the study prematurely during the first 6 months and 19 participants (10 from the telemetric group and 9 from the control group) during the second 6 months. According to the intention-to-treat principle, mean weight loss was 6.7 kg (p < 0,001), mean loss of body fat was 5.1 kg (p < 0,001), and mean loss of fat-free mass was 1.6 kg (p < 0,001) within the first six months. Moreover, metabolic and cardiovascular risk markers such as waist circumference, blood pressure, serum triglycerides and blood glucose declined significantly (p < 0,001). Prevalence of the metabolic syndrome fell from 49.5% to 42.0 % (p < 0,05). During the second six months body fat content, waist circumference, and blood glucose increased again in the control group but not in the telemetric group (p < 0,05-0,001). CONCLUSION: The telemetrically-guided weight loss program was a more efficacious measure than the less intensive support without telemonitoring.