BACKGROUND: The authors analyzed the trends in anthropometric and behavioral characteristics among patients seeking weight loss and the trends in choice of treatments, between 1997 and 2001 in an outpatient obesity clinic. PATIENTS AND METHODS: 138 and 128 consecutive patients attending the out-patient obesity clinic at University Hospital of Lausanne were screened in 1997 and in 2001 respectively. Eating habits, body composition and treatment used were assessed. RESULTS: Median BMI was 35 kg/m2 in 1997 and 38 kg/m2 in 2001 (P <0.001) and waist circumference was 99 cm and 111 cm respectively (P <0.001). This increase in the average body weight involved especially patients <30 years old (P <0.01). Morbid obesity increased by 16% (P <0.01), and prevalence of abdominal obesity by 13% (P < 0.05). The median desired weight loss increased significantly from 25% to 29% (P <0.05). 64% of the patients in 1997 and 83% in 2001 (P <0.01) hoped for a weight loss of 20% of their baseline weight. Motivation to lose weight for esthetic reasons was found in 81% of the women and 55% of the men in 1997 (P <0.01), while in 2001 the percentage was 89 and 43 respectively (P <0.001). CONCLUSION: In spite of the increasing access to weight loss programs, we found that the patients are more severely obese, especially those <30 years old, and have more unrealistic expectations of weight loss. This may explain the doubling of the patients treated by surgery.