Many diseases attributed to trafficking defects are primary disorders of protein folding and assembly. However, an increasing number of disease states are directly attributable to defects in trafficking machinery. In this context, the cytoplasmic coat protein (COP)II complex plays a pivotal role: it mediates the anterograde transport of correctly folded secretory cargo from the endoplasmic reticulum towards the Golgi apparatus. This review attempts to describe the involvement of COPII complex alteration in the pathogenesis of human genetic disorders; particularly, we will focus on two disorders, the Congenital Dyserythropoietic Anemia type II and the Combined Deficiency of Factor V and VIII. Am. J. Hematol., 88:135–140, 2013. © 2012 Wiley Periodicals, Inc.