A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems comprises the steps of taking the signal at the compensator output and extracting the components y.sub.1(t) and y.sub.2(t) on the two orthogonal polarizations, computing the signal y(t)=[y.sub.1(t)].sup.2+[y.sub.2(t)].sup.2, sampling the signal y(t) at instants t.sub.k=kT with T=symbol interval to obtain samples y(t.sub.k), computing the mean square error e(k)=y(t.sub.k)-u(k) with u(k) equal to the symbol transmitted, and adjusting the parameters of the compensator to seek to minimize e(k). A PMD compensator in accordance with the method comprises an adjustment system which comprises in turn a photodetecor (17) which takes the components y.sub.1(t) and y.sub.2(t) on the two orthogonal polarizations from the signal at the compensator output, a sampler (19) which samples at instants t.sub.k=kT with T=symbol interval, the signal y(t)=[y.sub.1(t)].sup.2+[y.sub.2(t)].sup.2 at the output of the photodetector (17) to obtain samples y(t.sub.k), a circuit (18, 20) for computation of the mean square error e(k)=y(t.sub.k)-u(k) with u(k) equal to the symbol transmitted, and a regulator (15, 16) which regulates the parameters of the compensator to seek to minimize e(k).