We assessed the prevalence and associations of symptoms of insomnia in patients with acute ischemic stroke, and evaluated whether mianserin as a sedative antidepressant is beneficial in the treatment of poststroke insomnia. One hundred consecutively hospitalized patients were randomized to receive 60 mg/day of mianserin (n = 51) or placebo for 1 year in a double-blind trial with a 6-month follow-up after the therapy. Symptoms of insomnia were assessed with the three insomnia-related items of the Hamilton Depression Scale; patients were defined as insomniacs if any of these items was positive. Complaints of insomnia occurred in 68% of patients on admission, and in 49% at 18 months, and they were as frequent in all subgroups of patients. From 2 months, symptoms of insomnia were associated independently with depression. Living alone before stroke (at 0 and 2 months) and age (at 12 months) were other independent predictors of insomnia. The rate of recovery as evaluated by the insomnia score was more rapid in patients on mianserin than in those on placebo. At 2 months, the scores were significantly different favoring mianserin treatment (1.3 vs. 0.8, p = 0.02). We conclude that insomnia is a common complaint after ischemic stroke. Mianserin had a beneficial influence on the recovery from symptoms of insomnia, even though the intensity of poststroke depression was low.