Lipid and carbohydrate metabolism are, amongst others, under the control of the neuroendocrine factors growth hormone (GH) and glucocorticoids (GC). A deregulation of either pathway has been associated with metabolic disorders including non-alcoholic fatty liver disease (NAFLD) in mouse models and humans. GH-activated signal transducer and activator of transcription (STAT) 5 and the glucocorticoid receptor (GR) were further shown to synergistically mediate the transcription of distinct GH target genes involved in hepatic sexual dimorphism. Here, we aimed to characterize STAT5's functions in liver metabolism, NAFLD and liver cancer development using two different approaches: 1) Targeted deletion of Stat5, Gr or both transcription factors in murine liver to investigate STAT5's function, particularly in context of an interaction with the GR. 2) Targeted deletion of hepatic Stat5 in a GH transgenic mouse model of inflammation-related hepatocellular carcinoma (HCC). Liver-specific GR deficiency was not associated with apparent alterations in hepatic lipid metabolism despite pronounced systemic hypercortisolism. Hepatic STAT5 deficiency, however, resulted in an early onset but stable steatotic phenotype associated with hepatic GH resistance and decreased insulin sensitivity. Genes involved in de novo lipogenesis and fatty acid uptake were induced, likely due to aberrant expression of their upstream activators proliferator activated receptor gamma (PPAR[gamma]) and sterol regulatory element binding protein 1c (SREBP-1c). GH was further shown to down-regulate Srebf mRNA expression and to mediate STAT5 binding to responsive elements within Srebf promoter regions in vivo. The stable steatotic phenotype was severely aggravated upon co-deficiency with hepatic GR or upon GH overexpression. ^More than 50% of 12-month-old STAT5 and GR co-deficient mice presented spontaneous HCC, while STAT5 deficiency strongly accelerated HCC development and progression in the GH transgenic background (100% penetrance, 40 versus 52-60 weeks of age). The aggrevated phenotype of both mouse models could be linked to enhanced adipose tissue lipid mobilization in response to high circulating GC and/or GH level and a drastic increase in ectopic lipids in liver. The hereby induced metabolic toxicity led to hepatocellular and DNA damage associated with oncogenic c-Jun N-terminal kinase 1 (JNK1) and STAT3 activation, whereas tumor-suppressive p53 activity was diminished. In two follow-up studies, we could further demonstrate that genetic inactivation of GC-GR or GH-STAT5 signaling in mouse adipose tissue diminished the lipolytic response of white adipocytes, ameliorated fasting-induced hepatic lipid deposition and increased insulin sensitivity. Thus, our data suggest a protective role of hepatic STAT5 signaling in NAFLD development and progression independently of GR function. Impairment of either transcription factor in white adipose tissue, vice versa, protects from ectopic hepatic lipid deposition.