Empirical antimicrobial therapy for lung abscess commonly includes anaerobic coverage, although evidence supporting its clinical benefit remains limited. We investigated the association between the extent of anaerobic coverage in initial therapy and clinical outcomes using the Japanese Diagnosis Procedure Combination database. Adults hospitalized between April 2022 and March 2023 with lung abscess (ICD-10 J85.2) were classified according to whether the initial antimicrobial regimen provided limited or extended anaerobic coverage and was continued for at least 3 consecutive days. Among 2800 patients, 161 received limited coverage, and 2639 received extended coverage. After propensity score matching, 161 patients in each group were compared. There were no significant differences in 30-day in-hospital mortality (6.2% vs. 6.2%), overall in-hospital mortality (12.4% vs. 10.6%), or length of hospital stay. Findings were broadly consistent across inverse probability of treatment weighting analyses and a sensitivity analysis using an alternative exposure definition based on the antimicrobial regimen administered on hospital day 1. We found no statistically significant evidence that extended anaerobic coverage was associated with improved clinical outcomes, although clinically important differences cannot be excluded.