Background: Hypophosphatemia is an increasingly recognized side-effect of ferric carboxymaltose (FCM) and possibly iron isomaltoside/ferric derisomaltose (IIM), which are used to treat iron deficiency. Objective: To determine frequency, severity, duration and risk factors of incident hypophosphatemia after treatment with FCM and IIM. Data Sources: A systematic literature search for articles indexed in EMBASE, PubMed and Web of Science in years 2005 to 2020 was carried out using the search terms ‘ferric carboxymaltose’ OR ‘iron isomaltoside’. Study Selection: Prospective clinical trials reporting outcomes on hypophosphatemia rate, mean nadir serum phosphate and/or change in mean serum phosphate from baseline were selected. Data Extraction: Hypophosphatemia rate and severity were compared for studies on IIM vs. FCM after stratification for chronic kidney disease. Meta-regression analysis was used to investigate risk factors for hypophosphatemia. Results: Across the 42 clinical trials included in the meta-analysis, FCM induced a significantly higher incidence of hypophosphatemia than IIM (47%, 95% CI 36-58% vs. 4%, 95% CI 2-5%), and significantly greater mean decreases in serum phosphate (0.40 versus 0.06 mmol/L). Hypophosphatemia persisted at the end of the study periods (maximum 3 months) in up to 45% of patients treated with FCM. Meta-regression analysis identified low baseline serum ferritin and transferrin saturation, and normal kidney function as significant predictors of hypophosphatemia. Interpretation: FCM is associated with a high risk of hypophosphatemia, which does not resolve for at least 3 months in a large proportion of affected patients. More severe iron deficiency and normal kidney function are risk factors for hypophosphatemia.