The problem of thickness dependence of dielectric and ferroelectric properties of Pb(Zr0.54Ti0.46)O3 (PZT) thin film capacitors is addressed. Experimental data collected on PZT capacitors with different thicknesses and different electrode configurations, using platinum and LaNiO3 conducting oxide, are examined within the prism of existing models. Available literature data, abounding but contradictory, led us to conclude that in the range of thickness investigated, size effect under all its aspects, i.e., increase in coercive field (Ec) as well as decrease in both dielectric permittivity and remnant polarization (Pr), result basically from existence of a depolarization field. It is shown however that the latter arises from interface chemistry, mostly related to the upper surface of the films, instead of finite screening length in the electrodes unlike commonly accepted. Moreover it is established that increase in Ec and decrease in Pr are not concomitant, and significant degradation of one or the other of these values strongly depends on whether a static potential, due to charged defects, is present or not at this interface.