The law, which took effect in April 1975, was prompted by concern with substantial increases in reported rapes that seldom resulted in successful prosecution. The law restricted the use of sexual history evidence, defined four degrees of sexual assault, eliminated the resistance and consent standards, and extended protection to such groups as males and legally separated spouses. Data for the present study included crime statistics and results of interviews with 170 criminal justice personnel and rape crisis center staff from 6 Michigan counties. Results indicated that the law did not affect reporting but was related to increases in arrests and convictions. Respondents also overwhelmingly agreed that a victim's experience with criminal justice processing was less traumatic after the law reform. The law also succeeded in bringing a wider range of cases to the system's attention. Respondents credit the shifts in the burden of proof resulting from the new law with responsibility for these positive changes. The law's neutrality with regard to sex and its degree structure also increase the likelihood of successful prosecution. Results were consistent across all the counties sampled. It was concluded that the law has achieved its goals. Factors responsible for its effectiveness include the criminal justice system's familiarity with the law, the law's reduction of discretion by criminal justice system personnel, its advantages to those implementing it, and its visibility. A risk exists, however, that the law's passage will be viewed as a solution and will dull sensitivities to unresolved social problems. Notes, a table, and four figures are included.