6H-SiC single crystals have been irradiated with 3 MeV electrons at a temperature of 200 K creating mainly vacancies on the carbon and the silicon sublattices. Positron annihilation experiments show that only well defined point defects have appeared. The influence of electron irradiation and of subsequent annealing on the lattice constants was studied by x-ray diffraction. An increase of the lattice constants by a relative value of 6.10(-5) due to the irradiation with a fluence of 1.8.10(19) cm(-2) was observed. Annealing at 1000 degreesC in Ar atmosphere leads to a regain of the pre-irradiation values. Furthermore, the spread of lattice parameters present in the as-grown samples is reduced after irradiation and annealing. Higher annealing temperatures up to 1850 degreesC do not lead to further changes.