Background: Stroke patients are particularly vulnerable to delirium episodes, but very little is known about its subsequent adverse mental health outcomes. The author’s objective was to explore the association between in-hospital delirium and depression, anxiety, anger and apathy after stroke. Methods: A total of 750 consecutive patients with acute stroke or transient ischemic attack, were screened for delirium during hospitalization. Patients underwent mental health evaluation in hospital, 3 and 12 months post-stroke; depression, apathy, anxiety and anger were the outcomes measured at all evaluation check points. Results: Delirium was an independent risk factor for depression (OR = 2.28, 95%CI 1.15–4.51, p = 0.017) and aggression (OR = 3.39, 95%CI 1.48–7.73, p = 0.004) at the hospital, for anxiety 3 months post-stroke (OR = 2.83, 95%CI 1.25–6.39, p = 0.012), and for apathy at the hospital (OR = 4.82, 95%CI 2.25–10.47, p < 0.001), after 3 (OR = 3.84, 95%CI 1.31–11.21, p = 0.014) and 12 months (OR = 4.95, 95%CI 1.68–14.54, p = 0.004) post stroke. Conclusions: The results of this study confirm, that mental health problems are very frequent complications of stroke. Delirium in the acute phase of stroke influences mental health of patients. This effect is especially significant in the first months post-stroke and vanishes with time, which suggests that in-hospital delirium might not be a damaging occurrence in most measures of mental health problems from a long-term perspective.