In this paper, we present a parametric fault diagnosis approach for analog/RF circuits based on a Bayesian framework. The Bayesian fault diagnosis requires extensive statistical profiling which is enabled by a an efficient hierarchical process variability analysis. Both DC and AC parameters are used as measurements to provide maximum diagnostic resolution. A sensitivity guided test input selection scheme is used to determine the measurement attributes that are most likely to distinguish among the faults. Fault dictionaries are constructed using parametric faults at the transistor level that have both marginal and higher deviations. During the diagnosis step, additional online profiling helps increase the diagnostic resolution. Experiments on a transistor level amplifier circuit confirms that the approach is accurate in terms of statistical attributes and most deviations in layout and process level parameters can be correctly diagnosed.