BACKGROUND The efficacy of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) differs in patients with lung adenocarcinoma harboring EGFR-activating mutations. Although lung adenocarcinoma with EGFR-activating mutations has heterogeneous morphologic features, the predictive role of histologic subtype of lung adenocarcinoma with regard to the effectiveness of EGFR-TKIs in patients with EGFR-activating mutations has not been well defined. METHODS Among 134 postoperative recurrence patients with lung adenocarcinoma harboring EGFR-activating mutation (L858R or exon 19 deletion) treated with EGFR-TKIs, we retrospectively analyzed 61 patients treated with EGFR-TKIs as first-line chemotherapy. All the tumors were classified according to the new histologic classification proposed by the International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS), and European Respiratory Society (ERS) into the following subtypes: lepidic, papillary, acinar, micropapillary, or solid predominant subtype. We evaluated the correlation between the histologic subtype and the clinical efficacy of EGFR-TKIs. RESULTS In overall response rate, adenocarcinoma with solid predominant subtype is significantly worse than with non-solid predominant subtype (61 vs. 88 %, P = 0.03). The median progression-free survival (PFS) and overall survival after EGFR-TKI treatment were significantly shorter for the patients with solid predominant subtype than for those with non-solid predominant subtype (median PFS of 7.7 vs. 13.5 months, P = 0.002, and median OS of 21.5 vs. 31.0 months, P = 0.028). CONCLUSIONS This study indicated that among patients with lung adenocarcinoma harboring activating EGFR mutations treated with EGFR-TKIs, solid predominant subtype according to IASLC/ATS/ERS classification is a response predictor for EGFR-TKI.