Multiple enzymes with overlapping functions and shared substrates in the glutathione (GSH) metabolic pathway have been associated with host susceptibility to tobacco smoke carcinogens and in lung cancer etiology. However, few studies have investigated the differing and interacting roles of GSH pathway enzymes with tobacco smoke exposure on lung cancer risk in young (<50 years of age) and old (>80 years of age) populations. Between 1997 and 2001, 237 primary lung cancer patients (170 young, 67 old) and 234 controls (165 young, 69 old) were enrolled at the Mayo Clinic. Using PCR amplification of genomic DNA, polymorphic markers for gammaGCS, GPX1, GSTP1 (I105V and A114V), GSTM1 and GSTT1 were genotyped. Recursive partitioning and logistic regression models were used to build binary classification trees and to estimate odds ratios (OR) and 95% confidence intervals for each splitting factor. For the young age group, cigarette smoking had the greatest association with lung cancer (OR = 3.3). For never smokers, the dividing factors of recursive partitioning were GSTT1 (OR = 1.7), GPX1 (OR = 0.6) and GSTM1 (OR = 4.3). For the old age group, smoking had the greatest association with lung cancer (OR = 3.6). For smokers, the dividing factors were GPX1 (OR = 3.3) and GSTP1 (I105V) (OR = 4.1). Results from logistic regression analyses supported the results from RPART models. GSH pathway genes are associated with lung cancer development in young and old populations through differing interactions with cigarette smoking and family history. Carefully evaluating multiple levels of gene-environment and gene-gene interactions is critical in assessing lung cancer risk.