Crack users increased their involvement in violent and property crimes but not drug use in the year following first use. For drug sellers, the effects of crack initiation on drug involvement and nondrug crimes were weaker than for users. Females significantly increased their involvement in prostitution after first crack use. For each type of drug or nondrug involvement, prior involvement was the most salient predictor of involvement in that behavior in the year following crack initiation. Results suggest that the influence of crack is independent of other behaviors rather than interactive, and weak overall. Crack initiation evidently intensifies prior behavior, rather than creating motivations or propensities for new behaviors. The report includes data concerning crack's effects on subjects' physical health, mental health, behavioral problems, and financial health. Notes, references, tables, appendixes