Lung adenocarcinoma has become the predominant histological subtype of lung cancer in many settings, particularly among women, but recent data from Peru are limited. This retrospective observational study analyzed anonymized records of 1,545 patients with histologically confirmed primary lung cancer treated at the National Institute of Neoplastic Diseases in Lima between January 2020 and December 2024. Demographic and clinical characteristics were summarized, the association between sex and adenocarcinoma was assessed using Pearson’s chi-square test, and multivariable logistic regression was used to estimate adjusted odds ratios (ORs). Women accounted for 60.0% of cases,and adenocarcinoma represented 61.29% of all diagnoses. Adenocarcinoma was more frequent among women than men (64.5% vs. 56.5%; χ² = 9.49, p = 0.002). In the adjusted model, female sex was associated with higher odds of adenocarcinoma (OR = 1.38, 95% CI: 1.12–1.70, p = 0.002). Age and geographic areas were also associated with adenocarcinoma, whereas year of diagnosis was not. The annual proportion among women varied, declining in 2021–2022 and increasing again through 2024. These institutional data indicate sex-related differences in histological distribution, but the retrospective design and lack of information on smoking, molecular markers, and individual exposures limit causal interpretation.