The crystallization behaviour of seven fractions of a copolymer of propene and l-hexane has been analysed. The fractionation discriminates simultaneously in comonomer content, stereoregularity and molecular weight, in such a way that the fraction obtained first at the lowest temperature displays the lowest molecular weight and isotactic triads fraction and the highest comonomer content. The crystallization rate of this fraction is very slow and it does not crystallize in the calorimeter when cooled from the melt at usual rates. The variation of different thermal parameters with the composition of these fractions has been analysed, as well as the crystallinity, determined by differential scanning calorimetry, X-ray diffraction and density measurements. Isothermal experiments enable us to obtain the extrapolated melting temperatures of these fractions and the Avrami exponent for the crystallization, which has been found to be close to three in all the cases. Non-isothermal experiments have also been analysed, comparing the results with the isothermal ones.