Abstract The longevity of patients with chronic lymphocytic leukemia (CLL) has improved progressively over the past decades, making it essential to understand long-term health outcomes, such as second primary malignancies (SPMs). Therefore, this nationwide, population-based study assessed the risk of SPM development in CLL patients diagnosed during 1989-2019 in the Netherlands compared to the expected number of malignancies in an age-, sex-, and period-matched group from the general Dutch population. In 24,815 CLL patients followed for 162,698.49 person-years, 4369 SPMs were diagnosed with a standardized incidence ratio (SIR) of 1.63 (95% confidence interval [CI] 1.59–1.68). This elevated risk was observed for solid (SIR, 1.67; 95% CI, 1.65–1.75) and hematological SPMs (SIR 1.42; 95% CI, 1.24–1.62). The highest risk for SPMs was noted beyond five years post-diagnosis (SIR, 1.70; 95% CI, 1.62–1.77), for male individuals (SIR, 1.70; 95% CI, 1.64–1.77), and patients aged 18–69 years (SIR, 1.92; 95% CI, 1.79–2.05). The risk of SPMs was higher in CLL patients who received anti-neoplastic therapy (SIR, 2.12; 95% CI, 1.96–2.28), as compared with those who did not (SIR, 1.58; 95% CI, 1.53–1.63). Routine surveillance activities and tailored interventions to counteract the increased morbidity and excess mortality associated with SPMs are essential for improving long-term outcomes in CLL patients.