Purpose Clinically significant pocket hematoma (CSH) is a common complication to cardiac implantable electronic device (CIED) surgery. We aimed to evaluate predictors of CSH after CIED surgery. Methods We performed a nationwide population‐based prospective cohort study with systematic patient chart review of all Danish patients undergoing CIED surgery during a 12‐month period. Multiple logistic regression analysis was used to estimate adjusted odds ratios (aOR) with 95% confidence intervals for association between predictors and CSH. Results We included 5918 consecutive patients, 63% males, mean age 72.6 years. A total of 148 (2.5%) patients experienced CSH, including 10 patients (0.2%) requiring re‐operation with hematoma evacuation. The risk of CSH was significantly increased in patients treated with aspirin (aOR 1.8; 1.2–2.7), aspirin and clopidogrel (aOR 3.9; 2.3–6.5), or heparin (aOR 2.1; 1.1–4.1), and in patients with INR≥2.0 (aOR 2.0; 1.2–3.2). Patients operated by low‐volume operators (aOR 2.7; 1.6–4.6) or undergoing more complex CIED surgery such as cardiac resynchronization therapy (aOR 2.0; 1.1–3.5) or dual‐chamber defibrillator (aOR 2.1; 1.2–3.8) also had significantly increased CSH risk. Conclusion In a large nationwide cohort of consecutive patients undergoing CIED surgery, the risk of CSH was 2.5%, with 0.2% necessitating evacuation. CSH risk was increased both in patients receiving aspirin, dual antiplatelet therapy or continued vitamin K‐antagonist therapy. Dual antiplatelet therapy had the highest risk (aOR) of CSH. Both low operator volume and more complex CIED surgery were independently associated with higher CSH risk. These data should be considered when planning CIED surgery.