The genus Corylus, a member of the birch family Betulaceae, includes several species that are widely distributed throughout temperate regions of the Northern Hemisphere. The development of microsatellites or simple sequence repeats (SSRs) for non-coding regions of the chloroplast genome and their higher sequence variation compared with coding regions has provided a higher resolution tool for the study of cultivars and closely related taxa. Chloroplast polymorphisms provide a marker system to evaluate the genetic structure of plant populations. This study investigated genetic diversity in three cultivars and 32 genotypes of Corylus avellana L. from Portugal: 13 wild genotypes and 19 Portuguese landraces. Four of ten cpSSR loci were polymorphic, with diversity indices ranging from 0.111 to 0.244. Eleven chlorotypes were detected, and their relationships were analyzed using a network model. Haplotype A was most frequent in landraces and cultivars. Four chlorotypes (H, I, J and L) were found only in wild hazelnuts. The diversity of chlorotypes in the wild hazels, and the limited number reported in cultivars, suggests that northern Portugal was a refuge for hazel during the last ice age.