In this paper, we analyze the effect of jitter in track and hold circuits. The output spectrum is obtained in terms of the system function of the track and hold. It is a fairly general model in which the effect of input as well as clock jitter can be included. The clock can have an arbitrary duty cycle, so that the circuit could also approximate a sample and hold. Using this model, it is possible to simulate the effects of jitter in a track and hold using a standard circuit simulator. Three cases are analyzed - long term jitter, correlated jitter with exponential autocorrelation and white noise jitter. These results are verified using Monte Carlo simulations. Copyright 2005 ACM.