The purpose of our study was to evaluate the frequency of leukocyte count abnormalities in a large cohort of SLE patients and its association with infection. To make this evaluation, we studied consecutive patients with SLE diagnosis and prospectively followed them in the Coimbra Lupus Cohort. Data about white blood cell count abnormalities and infection during one-year follow-up were obtained. The presence of leukopenia, lymphopenia, and neutropenia was registered for one-year period. Infections were classified as severe or mild. We found that of the 124 patients who were included (91.1% female, mean age 41.2, mean disease duration 11.1), mild infections occurred in 43.5%, and severe in 3.2% of the patients. Twelve percent, 41.1%, and 4.8% of the patients had persistent leukopenia, lymphopenia, and neutropenia, respectively. Fourteen percent received a pneumococcal vaccination. Patients with neutropenia had a significantly higher number of infections (P = 0.033). Thus, our study showed that neutropenia was associated with an increased risk of infection during this one-year follow-up. Infections were frequent, but most of them were mild.