Infection is a leading cause of death in the SLE population. Low immunoglobulin levels might be a potential risk for infection. We aimed to assess whether acquired low levels of any type of immunoglobulin increase the risk of clinically relevant infection in adult patients with SLE.We compared adult SLE patients who had acquired any low immunoglobulin levels (IgA, IgM or IgG) for 2 years with patients with normal or high levels with respect to clinically relevant infection (defined as infections requiring intravenous or oral antibiotics) in a prospective cohort study. Group balance was achieved using propensity score adjustment, matching and inverse probability weighting. Primary analysis was time to event using Cox-regression modelling adjusting for potential confounders. Sensitivity analyses were conducted to examine several exposure and outcome definitions.Patients with hypogammaglobulinaemia had longer disease duration, more lupus nephritis history, higher proteinuria and more accumulated damage. Low IgA level was associated with increased risk of clinically relevant infection [hazard ratio (HR): 2.24, 95% CI: 1.61, 3.12] while low IgG (HR: 1.15, 95% CI: 0.84, 1.59) or low IgM (HR: 0.95, 95% CI: 0.73, 1.23) was not. Low immunoglobulin recovery in the first year was 2.5% (11), second year 8.2% (36), third year 10.1% (44) and fourth year 18.4% (80), and 60% (263) of acquired hypogammaglobulinaemia recovered over 4 years.The majority of acquired hypogammaglobulinaemia in adult patients with SLE is transient. Only low acquired IgA was associated with increased risk of infection among adult patients with SLE. Whether immunoglobulin replacement provides additional protective effect requires further investigation.