OBJECTIVETo analyze the current situation of semenarche in boys aged 11 - 18 of 18 Chinese ethnic minority, and compare the average age of semenarche with Chinese Han boys from the same province or autonomous region.

METHODSThe average age of semenarche in various ethnic minority groups of Chinese boys who participated in 2005 National Physical Fitness and Health Surveillance were calculated. The sample size of ethnic minority boys was 16 267, and the ethnic minorities were Mongolian, Hui, Tibetan, Korean, Zhuang, Miao, Buyi, Dong, Shui, Tujia, Bai, Hani, Dai, Lisu, Wa, Naxi, Li and Tu. The local Han boys semenarche were also surveyed in 2005 National Physical Fitness and Health Surveillance. Probability unit regression, chi2 test, U test and dynamic clustering were used to calculate and analyze the average age of semenarche.

RESULTSIn the 13 years old group,the percentage of semenarche in Dong was lowest (5.00%, 5/100), while that in Li was the highest (68.35%, 54/79) (P<0.01). In the 14 and 15 years old group,the percentages of semenarche in Shui were the lowest (17.02%, 16/94; 22.83%, 21/92, respectively) (all P values <0.01), while the percentages in Zhuang were the highest (94.33%, 183/194; 98.45%, 191/194, respectively).When reached 18 years old, 97.85% (2137/2184) ethnic minority boys experienced semenarche. The top 3 ethnic minority groups in average age of semenarche were Korean (12.37 years old), Zhuang (13.34 years old) and Naxi (13.36 years old); and the last 3 ethnic minority groups were Shui (16.19 years old), Bai (15.27 years old) and Tu (15.19 years old). The average age of semenarche in Zhuang was 1.34 years earlier than that of Han boys from Guangxi Zhuang autonomous region; the average age in Korean was 1.28 years earlier than that of Han boys from Jilin province; and the average ages in Naxi and Dai were 0. 89 years and 0. 17 years earlier than that of Han boys from Yunnan province, respectively (all P values < 0. 01). The cluster analysis indicated that the 18 ethnic minority groups could be classified into two groups: Zhuang, Naxi, Li and Korean were classified into earlier age group of semenarche, and the other 14 ethnic minority groups were belonged to later age group of semenarche.

CONCLUSIONThere was a large variation among different ethnic minority groups in terms of average age of semenarche. The semenarche was earlier in Zhuang, Korean, Naxi, and Dai, compared with local Han boys.