A new method for the testing and fault detection of analog integrated circuits is presented. Time-domain testing followed by spectral analysis of the power-supply current is used to detect both DC and AC faults. Spectral analysis is applied since the tolerances on the circuit parameters make a direct comparison of waveforms impossible. For the fault detection a probabilistic decision rule is proposed based on a multivariate statistical analysis. Since no extra testing pin is needed and the on-line calculation effort is small, the method can be used for wafer-probe testing as well as final production testing. In addition, a methodology for the selection of the input stimulus is presented that improves the test-ability. Examples demonstrate the efficiency and the effectiveness of the algorithms.