Background: Patients with squamous cell carcinoma (SqCC) of the lung sometimes have a comorbid pulmonary disease such as pulmonary emphysema or an interstitial lung disease (ILD), both of which negatively affect patient outcome. The aim of this study was to determine the outcome of patients in a multicenter database who underwent surgery for cT1aN0M0 peripheral SqCC lung cancer. Methods: The medical records of a total of 228 eligible patients from seven institutions were reviewed to evaluate the impact of concomitant impaired pulmonary function and other clinicopathological factors on overall survival (OS) and relapse-free survival (RFS). Results: Six patients with positive or unclear tumor margins were excluded. Of the 222 remaining study patients, 42 (18.9%) and 97 (43.7%) patients were found to have coexisting restrictive or obstructive ventilatory impairment, respectively. Over a median follow-up period of 30.6 months, the 5-year OS and RFS were 69.0% and 62.6%, respectively. By multivariate analysis, ILDs identified on high-resolution computed tomography (HRCT), pulmonary function test results indicating a restrictive ventilatory impairment, and wedge resection were found to be independent risk factors for poor OS. An increased level of serum squamous cell carcinoma antigen (SCC-Ag) (>1.5 ng/mL) and the same risk factors for poor OS were independent risk factors for recurrence. Among patients who underwent anatomical lung resection (lobectomy and segmentectomy, n=173), a restrictive ventilatory impairment was an independent risk factor for poor OS, and increased serum SCC-Ag level, ILDs on HRCT, and restrictive ventilatory impairment were independent risk factors for poor RFS by multivariate analysis. Factors such as visceral pleural invasion, and lymphatic or vascular invasion were not significantly associated with outcome. Conclusions: A restrictive ventilatory impairment negatively affects the outcome of patients with cT1aN0M0 peripheral SqCC lung cancer.