Abstract Body (Do not enter title and authors here): Using the translationally relevant sheep model of prenatal testosterone (T) excess, we previously reported intrauterine growth retardation (IUGR) in both sexes, adverse sex specific programming of fetal heart and cardiometabolic dysfunction in adult female offspring. Because of the intricate reciprocal relationship between the heart and lungs, we hypothesized that gestational T excess will have detrimental sex-specific effects on offspring lungs beginning as early as fetal life and extending into adulthood. Pregnant ewes were intramuscularly injected with 100 mg of testosterone propionate twice weekly from gestational days (GD) 30-90 (term 147 days) and offspring lungs were harvested at GD120, 30 days after cessation of T treatment; (n=4-7/group) and in adulthood (n=4-6/group) and processed for molecular and histological analyses. Data was analyzed by student T test within each sex and Cohen (d) effect size was calculated (Cohens d>0.8 represents large effect size. Lung collagen was significantly increased in T-male fetuses (TM) vs control males (CM) (p=0.01, d=1.99) that persisted into adulthood (TM vs CM: p=0.01, d=1.83). The effects of gestational T excess was evidenced as an increase in collagen only in the lungs of adult T-female fetuses (TF) relative to control females (CF) (p=0.003, d=2.38), but not during fetal life. Gestational T excess induced significant parallel increases in TUNEL positive nuclei/frame in TM fetuses relative to CM (n=3/group, p=0.01, d=3.35) persisting as a large magnitude increase of TUNEL positive nuclei/frame in adult TM (p=0.12, d=0.96). In TF females, apoptotic changes were not noted in fetal lungs but an increase of TUNEL positive nuclei/frame was evidenced in adult TF (p=0.08, d=1.14). At the molecular level prenatal T excess induced an increase in histone deacetylase 1 (HDAC1) expression in fetal TM vs CM (p=0.04, d=1.50), and decrease in HDAC1 in TF vs CF (p=0.10, d=1.09) suggestive of T-induced epigenetic alteration. Transcriptomic analysis of fetal lungs revealed upregulation of pathways associated with estrogen signaling and neuroactive ligand receptor interaction, and downregulation of pathways associated with protein processing in endoplasmic reticulum and antigen processing & presentation (unadjusted p< 0.05, log FC>1.5) in both sexes. Overall, early to mid-gestational exposure to testosterone adversely reprograms the lungs in sex specific fashion as early as fetal life extending into postnatal adult life.