The results of the research on the accuracy of the periodic discrete-time signal reconstruction by means of trigonometric interpolation are presented. It is found that the dependence of mean square error of trigonometric interpolation on the number of signal samples is an additive mix of monotonously decreasing function of the number of samples and some periodic function of number of samples. It is shown that in defiance of classical estimates of a trigonometric interpolation error, existence of a periodic component leads to the fact that formal increase in number of samples can lead to reduction of reconstruction accuracy of continuous signal.