In a randomized controlled trial, we compared the efficacy of topiramate versus placebo in women undergoing olanzapine therapy and found that topiramate effectively contributed to weight loss in short-term treatment and had a positive effect on health-related quality of life, the patients' actual state of health, and psychological impairments. The aim of this observational study was to assess whether topiramate has a sustained benefit in long-term treatment of olanzapine-associated weight gain in subjects who had participated in the previous randomized controlled trial comparing topiramate with placebo. The subjects (topiramate group, n = 25; former placebo group, n = 18) were observed in an 18-month open-label study. After unblinding, subjects from the former topiramate group continued treatment with topiramate, whereas subjects from the former placebo group received neither placebo nor topiramate. The subjects were seen every 6 months, weighed, and tested with the SF-36 Health Survey, Scale of Well-Being, and the Adjective Checklist. According to the intent-to-treat principle, the repeated-measures analysis showed a significant interaction for the group-by-time effect for change of weight (P < 0.01) on the Scale of Well-Being (P < 0.01), all scales of the Adjective Checkist (all P < 0.01), and 5 scales (physical functioning, role limitations due to physical health, social functioning, mental health, and vitality) of the SF-36 Health Survey (all P < 0.01). Topiramate was well tolerated and seems to be effective and safe in the long-term treatment of olanzapine-related adiposity in women. Furthermore, positive changes in the patients' state of health, psychological impairments, and health-related quality of life could be also observed.