The Karnataka Multisectoral Nutrition Pilot Project (2015–2018) was implemented in Devadurga Block, Raichur District and Chincholi Block, Gulbarga District—two most backward Blocks in Karnataka. Special interventions for behaviour change and appropriate dietary supplementation for adolescent girls (11–18 years) were implemented through an inter-sectoral, intergenerational strategy. This article analyses real time data regarding thinness/severe thinness among 8,847 adolescent girls in the cross-sectional group and 1,545 adolescent girls in the cohort group. Both BMI-cut-offs method and BMI-for-age Z-score methods provide strong evidence of significant increase in percentage of ‘normal’ adolescent girls from baseline to endline; significant decrease in severe thinness; non-significant decrease/increase in moderate thinness. Data also indicates that while 68.2% of baseline moderately thin girls transitioned to normal category, 71.8% new moderately thin girls (44.3% from improved severely thin girls and 27.5% from normal girls), transitioned into the moderately thin category. Data provides strong evidence that thinness/severe thinness among adolescent girls reduced significantly through project interventions, which are simple to replicate. Tallest girls at baseline, and those gaining fastest height, transitioned to becoming/remaining moderately/severely thin, an area for further research. Further research is required regarding the ideal duration of interventions to improve moderate underweight/thinness to normal status.