The age/crime relationship is explored by applying a time series-cross section model, using data from 1971-1988 for most states. The analysis includes year effects which indicate that yet unidentified nation wide factors are very important. Age structure was found to affect all seven types of index crime; although the results for murder, assault, and vehicle theft are only marginally significant. The high impact age groups are roughly similar to the high arrest groups, but they tend to be somewhat older and less concentrated in the peak years. Differences are most noticeable for vehicle theft. The results are interpreted as supporting the crime-opportunity theory and any attempts to estimate the impact of age structure must incorporate the impact of victims' age structure. This problem, along with the importance of year effects, lead to the conclusion that it is not useful to estimate the portion of crime trends attributable to age structure and that forecasts based on age structure trends are unlikely to be accurate. 11 tables and 120 references (Author abstract modified)