Background Approximately 10% to 15% of lung cancer cases in the United States occur in never smokers, but there has been much debate about whether this rate is increasing. To determine whether the proportion of never smokers among lung cancer cases is increasing, we conducted a retrospective study using registries from The University of Texas Southwestern Medical Center, Parkland Hospital, and Vanderbilt University. Methods Registries were queried for demographic information from 1990 to 2013 including sex, age, stage, and self-reported smoking history. Ten thousand five hundred ninety-three non-small cell lung cancer (NSCLC) case patients and 1510 small cell lung cancer (SCLC) case patients were captured, and logistic regression analysis was performed. All statistical tests were two-sided. Results The proportion of never-smoker NSCLC patients increased from 8.0% in the years 1990 to 1995 to 14.9% in 2011 to 2013 (P < .001). This increase was also observed using multivariable logistic regression after controlling for sex, stage at diagnosis, and race/ethnicity. The percentage of never smokers among SCLC case patients (1.5% in 1990-1995 to 2.5% in 2011-2013, P = .36) or squamous cell NSCLC case patients did not statistically significantly change during this period. Conclusions This study demonstrates an increasing proportion of NSCLC patients who have never smoked in a large, diverse patient population between 1990 and 2013. Given that this increase appears independent of sex, stage, and race/ethnicity and also occurred in our county hospital, this trend is unlikely due to changes in referral patterns and suggests that the actual incidence of lung cancer in never smokers is increasing.