A number of studies of seismic refraction data have resulted in suggestions that the oceanic crust thickens with age, perhaps over a long time span. It is difficult to reconcile notions of crustal thickening with many of our ideas about crustal structure and formation. In this study we have re-evaluated data compiled from a number of sources to obtain crustal thickness and age parameters for 105 different refraction profiles in the Pacific. An attempt was made to exclude data which might have poorly determined values of crustal thickness. The crust does appear to thicken with age to 30 or 40 m.y., but the effect is very subtle. Once probable biases are removed from the data, crustal thickening is not significant to a 95% confidence limit if ten m.y. samples are used. However, if one takes sample intervals of 0-30 m.y. and 30-100 m.y. there appears to be some difference in the average crustal thickness. Even in the latter case, the amount of thickening is far less than previous studies have suggested, only .45 km. Thus evidence for the long-term addition of mass to the crust remains tenuous.