HIV/AIDS infection in injecting drug users occurs with explosive rapidity and, having occurred, they can form a core group for further sexual and vertical transmission. As HIV transmission among injecting drug users can be extremely rapid, various approaches to intervention and obstructing the spread of HIV infection have been explored. Overall, these have been relatively ineffective so what has emerged, both in the developed and developing world, is harm reduction. In the light of these general considerations, the authors reviewed the law of Thailand in relation to drug abuse and dependence according to the harm reduction for the prevention of HIV/AIDS infection in injecting drug users. With the review, the authors recommend some changes in the law: 1. Introducing a law that allows IDUs to possess sterile syringes and needles while under supervision of a physician. 2. Introducing a law that allows for testing for HIV in people in custody in whom there are grounds for suspecting drug abuses. 3. Establishing and financing a Multi-disciplinary Coordinating Committee on the Prevention of HIV/AIDS (MCCPH/A). It should be emphasized that, as in other countries, drug abuse and dependence should, where appropriate, be decriminalized. A large proportion of people with drug-related problems are ill and in need of treatment rather than criminals requiring harsh penalties handed down by the courts.