Surficial sediment samples were collected from 63 Illinois lakes during summer 1979. Samples were analyzed for organic matter, nutrients, heavy metals and organochlorine compounds. For purposes of statistical analysis, lakes were placed into one of several groups (glacial, artificial or miscellaneous). Most lakes were artificial reservoirs and these were subdivided based on geographic location. Spatial variations of glacial lake means were contrasted with artificial lake studies. In an attempt to correlate fish flesh pesticide concentrations with sediment concentrations, no simple linear relationships were discerned. In general, the low organic content of Illinois sediments was probably attributable to the high non-volatile suspended solids loading characteristic of most Illinois lakes. Regardless of organic carbon content, the ratio of C:N remained fairly constant at 14:1. The N:P ratio for Illinois lake sediment of 6:1 was somewhat less than the generally conceded 7:1 for plant material. Most Illinois lakes exhibited fairly low sediment metal/metalloid concentrations. Most chlorinated hydrocarbon pesticides were undetected or occurred at low levels in sediment samples. PCB's were detected only in sediments from seven of the lakes sampled. A classification of Illinois lake sediments based on mean constituent concentrations and respective standard deviations was developed to facilitate interpretation of sediment data. The resultant four tier classification system categorized lake sediments as below normal, normal, elevated, and highly elevated.