Hydrolytic degradation of electrospun mats of poly(L-lactic acid), PLLA, as a function of crystallinity and fiber diameter has been studied. The degradation in a saline phosphate buffer solution (PBS) up to 20 weeks produced a slight decrease in the sample mass but a clear decrease of the polymer average molecular weight in the amorphous fibers. This effect decreases as crystallinity increases. It is important for applications that morphological characteristics of the membranes such as average fiber diameter and membrane porosity are also affected by the degradation process. Fiber diameter increases while membrane porosity decreases, resulting in closer packed fibers due to the release of internal tensions related to the electrospinning and/or thermal treatment processes. (C) 2012 Elsevier Ltd. All rights reserved.