In the United States, insurance benefits for treating alcohol, drug abuse and mental health (ADM) problems have been much more limited than medical care benefits. To change that situation, more than 30 states were considering legislation that requires equal benefits for ADM and medical care ('parity') in the past year. Uncertainty about the cost consequences of such proposed legislation remains a major stumbling block. No information is available about the actual experience of implementing parity benefits under managed care or the effects on access to care and utilization. Ohio's experience with adopting full parity for ADM care within its state employee program is examined, using data from 1987 to 1997. The Ohio state case study demonstrates that parity level benefits for ADM care are affordable under managed care. The next step is to address quality of care or health outcomes, two areas less understood than costs.