OBJECTIVE To study the secular trend of menarche in high-school urban adolescent girls (Zagreb, Croatia) over the last two decades, and to evaluate the possible impact of worsening of socio-economic conditions on age at menarche during the Croatian War of Independence (1991-1995). METHODS Three surveys of female adolescents aged 15-19 years: (a) 523 girls interviewed in 1990, (b) 888 girls interviewed in 1997, and (c) 399 girls interviewed in 2010. Self-reported age at menarche (in decimal years) was presented by age groups and year of interview. Differences in mean age at menarche between adolescent age groups as well as between surveys were tested using One-way ANOVA. RESULTS The mean age at menarche was 12.82 years in 1990, 12.92 years in 1997 and 12.31 years in 2010. It increased by 0.10 years from 1990 to 1997 (p=0.290) and then declined by 0.61 years from 1997 to 2010 (p<0.001). Over the 20-year period, the overall mean age at menarche declined by 0.51 years (p<0.001). CONCLUSIONS The age at menarche in Zagreb adolescents continued to decline significantly from 1990 to 2010 (p<0.001), in spite of a statistically insignificant initial increase between 1990 and 1997. When put in broader context, age at menarche mirrored socio-economic changes in the war period.