Preadipocytes are multipotent adipogenic precursor cells that can be isolated from mature adipose tissue. They have been receiving increasing attention in the context of obesity, type 2 diabetes, and other nutrition-associated diseases. Understanding the physiological and pathophysiological processes in fat neo-formation, energy homeostasis, and adipose tissue physiology is the basis for research on metabolic diseases and the respective pharmaceutical intervention. While the hormonal influence on intracellular signaling in adipogenesis has been intensively investigated, the effects of free radical formation and oxidative stress have just started to gain scientific attention. This review summarizes the present knowledge on the main molecular pathways in preadipocyte maturation and focuses on recent findings indicating that besides hormonal stimuli reactive oxygen species (ROS) and free radicals may also interact with preadipocyte differentiation.