We studied 29 patients with major depression before treatment and then followed these patients prospectively with monthly electroencephalographic (EEG) sleep assessments after successful treatment. Most EEG sleep measures demonstrated no change from the episode throughout a prolonged period of clinical remission. When there was evidence of a change in EEG sleep measures, the effect was modest and due to only a small subset of patients. These findings contribute to the accumulating evidence that selected EEG sleep measures appear to be trait-like and may be useful in identifying individuals at risk for major depression.