Background: Stroke patients often have neuropsychiatric symptoms and cognitive deficits. The aim of this study was to investigate whether stroke patients with psychiatric symptoms are at increased risk of developing cognitive deficits. Methods: Cognitive function (assessed with a neuropsychological test battery) and presence of psychiatric symptoms (assessed with the 90-item Symptom Checklist) were evaluated at 1, 6, 12 and 24 months after stroke. Results: At baseline, 156 patients entered the study, 15 had a diagnosis of vascular dementia, 113 one of post-stroke mild cognitive impairment. Patients with psychiatric symptoms were found to be at increased risk of being diagnosed as having vascular dementia at baseline (OR = 6.9, CI = 1.3–36.8) and showed more decline on cognitive function 6 months after stroke. Conclusions: Patients with psychiatric symptoms after stroke are at increased risk of cognitive deficits and decline in cognitive functioning.