There are some evidences that hypogammaglobulinemia in newly diagnosed diffuse large B cell lymphoma (DLBCL) is a predictor for inferior outcome, but the risk for infection-related admissions specifically related to hypogammaglobulinemia is not known. The aim was to explore if hypogammaglobulinemia in untreated DLBCL in a Swedish cohort was associated with inferior outcome, and to assess the relationship between low immunoglobulin (Ig) levels and infections. Using data from the Swedish Lymphoma Register, we retrospectively identified patients above18 years diagnosed with DLBCL, receiving anthracycline-based curative therapy during 2000-2015 in Southern Sweden with Ig-levels tested at baseline. Data on Ig levels and infections were collected from medical records. Five hundred eighty-five patients were included, median age was 69 years. Hypogammaglobulinemia was detected at baseline in 24%, the most common Ig deficiency was IgG (18%), followed by IgA (10%) and IgM (8%). Hypogammaglobulinemia was associated with inferior overall survival (HR 1.4, 95% CI 1.0-1.8, p-value 0.018), but not when adjusted for International Prognostic Index (IPI). Low levels of Ig were associated with more infections during lymphoma treatment (p-value 0.013), also when adjusted for IPI (p-value < 0.001). Among patients with IgG deficiency, 47% had ≥ 1 infections versus 35% in patients with normal IgG (HR 1.2, p = 0.025). In conclusion, hypogammaglobulinemia was a frequent finding in patients with newly diagnosed DLBCL, with clinical impact in terms of treatment complications and outcome., (© 2024 John Wiley & Sons Ltd.)