Phosphodiesterase (PDE) 4 participates in regulating the inflammatory response by degrading cyclic adenosine 3'5'-monophosphate (cAMP), a key second messenger. Inhibition of PDE4 increases the intracellular cAMP level, which in turn results in a reduction in inflammatory mediators and an increase in anti-inflammatory mediators. Immune-modulating effects of PDE4 inhibitors have been investigated in a number of inflammatory conditions, such as asthma, atopic dermatitis, chronic obstructive pulmonary disease, Behçet’s disease, psoriasis, and psoriatic arthritis. Apremilast, a selective PDE4 inhibitor, has been shown to block the production of pro-inflammatory cytokines (interferon-γ, tumor necrosis factor-α, interleukin [IL]-12, IL-17, and IL-23), which are the key players in the pathogenesis of psoriasis. Increased intracellular cAMP levels result in a range of anti-inflammatory effects on numerous cell lines. A decrease in proinflammatory activity has been shown to result in a reduced psoriasiform response in preclinical in vivo models of psoriasis, and reduction of biologic activity in a pilot study in humans. The efficacy and safety of apremilast in the treatment of psoriasis have been demonstrated in phase II and III clinical trials. Apremilast demonstrated efficacy in reducing the severity of moderate to severe plaque psoriasis. Treatment with apremilast was well tolerated, with generally mild gastrointestinal complaints, which occurred early in the course of the treatment and resolved over time, and there was no requirement for laboratory test monitoring. These results make apremilast an attractive therapeutic option for plaque psoriasis.