To the Editor: The article by Leonardo Tondo, M.D., and Ross J. Baldessarini, M.D. (1), contains an obvious mistake. The authors report that we, Maj et al. (2), and Bauer et al. (3) found a rapid-cycling course of illness in 33.3% and 50.2%, respectively, of our patients with bipolar disorder. We found that pattern instead in 13.6% of the patients with bipolar disorder who were referred to our center (as clearly stated in the Results section of our article), and we recruited for our comparative study two patients with nonrapid cycling for each patient with rapid cycling. Similarly, Bauer et al., in their multisite study, did not find an unusually high proportion of patients with rapid cycling but simply asked each site to provide an equal number of patients with rapid cycling and patients with nonrapid cycling (as specified in the Method section of their article).