- OBJECTIVES: To determine what is known from the existing literature about empirical relationships between numeracy and the three stages of the treatment decision making process (information exchange, deliberation, and deciding on the treatment to implement). We also examined if, and how, numeracy was mentioned in relation to health literacy. METHODS: A search of four databases returned 2772 records. After de-duplication and three levels of relevance screening, 38 primary studies were included in this review. RESULTS: Relationships between numeracy and the information exchange stage have received greater attention than relationships between numeracy and the deliberation and deciding on the treatment to implement stages. The lack of overlap in the empirical relationships examined in studies, the measure(s) of numeracy used, and the characteristics of study populations, made findings difficult to compare. Multiple knowledge gaps and measurement-related problems were identified. Numeracy and health literacy have largely been treated as separate concepts. CONCLUSION: More research is needed to better understand the importance of numeracy and health literacy to treatment decision making. PRACTICE IMPLICATIONS: Decision aids designed for patients with different levels of health literacy may not meet the needs of patients with different levels of numeracy. The numeracy skills of health professionals require attention.