Leptin is a neuroendocrine peptide released by adipose tissue that enhances metabolism and acts on the hypothalamus to suppress appetite. Leptin also regulates aspects of cardiovascular function and low serum leptin has been associated with increased mortality in humans. We hypothesized that leptin deficiency alters the structure and function of the pulmonary vasculature. Methods: We examined two groups of C57BL/6 male mice aged 12 weeks: five ob/ob (B6.VLep(ob/ob)) leptin-deficient and five wild type (WT) (C57BL/6) control mice. As expected, weight was significantly greater in ob/ob mice relative to WT mice [weight (g), Mean +/- SD): ob/ob 52 +/- 2.5 g, wild type 30 +/- 2.5 g; p < 0.001]. The pulmonary vasculature of ob/ob mice and WT control animals was examined by histology, immunohistochemistry and immunofluorescence staining. Results: Pulmonary arterial wall thickness was significantly increased in ob/ob mice relative to WT littermates [median (interquartile range) distance in pixels: ob/ob 0.13 (0.05-0.18), wild type 0.03 (0.02-0.04); p = 0.001]. The ob/ob mice also exhibited significant right ventricular hypertrophy in comparison to control animals [RV thickness (Mean +/- SD): ob/ob 0.75 +/- 0.19, wild type; 0.58 +/- 0.13 p < 0.001]. We observed substantial macrophage infiltration and abundant proliferation of myofibroblasts and fibroblasts in histological sections of pulmonary arterioles of ob/ob mice. In addition, we noted increased hyaluronan deposition, colocalizing with SMC-actin in the pulmonary vasculature of ob/ob mice relative to WT controls. Conclusions: The pulmonary pathology of leptin deficiency in ob/ob mice recapitulates many of the histological features of pulmonary vascular diseases, including pulmonary hypertension, suggesting that leptin deficiency is associated to the pathogenesis of pulmonary vascular disease.