The objective was to determine both to what degree these crime rates correspond over time and the extent that changes in reporting to the police influenced annual UCR rates and thereby contributed to divergence between the two crime data series as well as to learn if the recent upturn in UCR crime rates is primarily attributable to increases in crime reporting or to underlying levels of criminal victimization. The differences between the two data series emerged primarily in their contrasting trends, but there was some evidence that trends in UCR and NCS crime rates have been converging in recent years. The UCR/NCS relationship estimated from the 1973-1985 data continued through 1986 and 1987. The UCR rates in 1986 were influenced somewhat by unusual increases in the proportion of crimes reported to the police that year, but changes in crime reporting for the period as a whole have had little effect on UCR burglary and robbery rates. Within the two serious crime types examined, there was strong consistency between the alternative data sources on variations in crime rates over time. 4 tables, 14 footnotes, and 34 references (Author abstract modified)