May 22 (Bloomberg) -- New HIV/AIDS cases in Japan reached 1,358 last year, the biggest annual increase in more than two decades, as men fail to heed warnings over the dangers of unprotected sex.

Last year, 952 people were diagnosed with HIV, the virus that cases AIDS, Japan's Ministry of Health, Labor and Welfare told reporters in Tokyo. An additional 406 patients developed AIDS, with men representing more than four of every five cases, the ministry said.

``Sexual contact among males continues to be the main reason for the increase'' in cases, said Aikichi Iwamoto, a professor of infectious diseases at the University of Tokyo, who led the research.

Japan had 12,394 HIV/AIDS cases as at Dec. 31 since it began collecting data on the disease in 1985, the health ministry said. Of those, 4,050 were diagnosed with AIDS, the ministry said.

To contact the reporters on this story: Kanoko Matsuyama in Tokyo at at kmatsuyama2@bloomberg.net

Last Updated: May 22, 2007 06:39 EDT