Mental health nursing for adults with intellectual disabilities and mental illness is underresearched. The aim of this review is to summarize empirical mental health nursing studies including adults with intellectual disabilities and additional mental illness. Out of 137 hits, 16 articles were reviewed in full text. Thirteen of the articles presented modified nursing interventions. Three articles discussed training and education. The main finding is that mental health nursing interventions in patients with intellectual disabilities and additional mental illness are in line with mental health nursing for the general population. There are still not many publications on empirical studies concerning mental health nursing for adults with intellectual disabilities. Clinical implications are primarily related to the need for facilitated nurse–patient communication adjusted to the patients' cognitive levels. Insights drawn from this review illuminate the importance of mental health nursing interventions adjusting to the particular patients' symptoms, instead of targeting behavior change. The findings underpin factors found to have a positive impact on patients with mental illness in the general population as relevant topics for future research.