The study aimed at clarifying basic life traits (fecundity, mortality and development) of Monochamus galloprovincialis, the vector of Bursaphelenchus xylophilus, the causative agent of the Pine Wilt Disease, in Portugal. Mating and oviposition experiments were conducted on P. sylvestris logs under laboratory conditions during two years. Larval development was followed outdoors. Fecundity was high, with 138.2 eggs per female. For the first time, the number of larval instars (4) in M. galloprovincialis was recognized and instars were described. Informations are provided on the shape and size of the larval galleries. Boring of galleries in sapwood and heartwood started at the third instar. All instars could overwinter but adults emerged simultaneously resulting in a univoltine life cycle for the majority of the individuals. An obligatory diapause in the forth instar was assumed. However, 8.1% of the insects had a two year development. Important differences in mortality were noted between the two experimental years, which could be explained by differences on the size of the breeding logs. There is a high biological proximity between M. galloprovincialis populations in France and those in Portugal and Northern Europe. However, a higher fecundity and longevity was observed in France, as well as a higher percentage of insects with a two year development, compared with portuguese populations.