Abstract Objective The effect of delirium on stroke outcome has not been quantified in sub-Saharan Africa. We investigated the prevalence of delirium occurring within one week of stroke in Nigerian survivors and its association with dementia and mortality at 3 months. Methods Delirium was ascertained after repeated assessments within one week of stroke using the Confusion Assessment Method. Demographic and clinical characteristics, stroke severity, current and pre-morbid cognitive functioning were also assessed. Participants were then followed up for 3 months using culturally-validated neuropsychological tools. Probable dementia was ascertained according to the National Institute of Neurological Disorders and Stroke (NINDS-AIREN) criteria. Associations were investigated using both binomial and multinomial logistic regression analyses and presented as odds ratios (O.R) and relative risk ratios (RRR). Results Of 101 consenting stroke survivors, 99 had two assessments for delirium within one week of the stroke. Delirium was present in 33.3% of stroke survivors (65.6% hypoactive, 21.9% hyperactive, and 12.1% mixed type). Having a severe stroke was associated with delirium (O.R = 6.2, 95% C.I = 1.1–13.8) after adjusting for age, gender, education and economic status, lifestyle factors, multimorbidities and laterality. At follow-up, those with severe stroke had a stronger association between delirium and dementia (RRR = 4.3, 95% C.I = 1.2–15.6) or death (RRR = 3.7, 95% C.I = 1.1–12.1). Conclusion Delirium was already present in about one-third of survivors within one week of stroke. Survivors of severe stroke are at higher risk of delirium and its complications, and could be important target for delirium preventive interventions.