Evidence on the use of complementary and alternative medicine (CAM) modalities in the treatment of depression, anxiety, sleep disorders, and attention-deficit/hyperactivity disorder (ADHD) is reviewed. There is strong evidence to support the use of St. John's wort (SJW) in depression, and growing support for the use of omega-3 fatty acids and S-adenosyl-l-methionine as potential adjuncts to conventional therapies. Evidence is insufficient to support the antidepressant benefit of dehydroepiandrosterone, inositol, folate, and saffron. Only kava has high-quality evidence for use in the treatment of anxiety disorders, and its use is discouraged because of safety concerns. There is preliminary supportive evidence for valerian and inositol treatment of anxiety, but SJW and passionflower have achieved little research support. Melatonin is likely to be useful in treating delayed sleep phase, jet lag, or shift work, but there is little evidence for the benefit of valerian compared with placebo. There are currently no evidence-supported CAM treatments for ADHD (zinc and omega-3 fatty acids are reviewed).