This study investigated the effect of post-treatment phone contact on weight-loss maintenance and activity behaviour in obese youngsters. In all, 20 patients who completed a weight reduction program were randomly assigned to a 5-month maintenance programme (experimental) or control condition. Following the maintenance programme, patients sent a weekly activity diary to the therapist, who in turn phoned them biweekly to discuss their activities. Body weight, stature and physical activity were measured before and after the maintenance programme. The control group showed a continuous increase in overweight after initial treatment, while the experimental group showed a steep increase during the summer holidays (no intervention), but this increase slowed down during the maintenance programme (P<0.05). Moderate-to-high intensity activities increased during the maintenance programme in the experimental group, but decreased in the control group (P<0.001). In conclusion, post-treatment phone contact appears to have the potential to be an effective maintenance strategy in obese youngsters.