Introduction– The Caries Assessment Spectrum and Treatment (CAST) Index – Frencken JE et al. (2011) records all the clinical stages of caries spectrum under 9 codes.  Objectives– Measure caries via CAST index in slum children. Method– Cross sectional study was done on 151 slum children in Udupi, by a single trained examiner using CAST index. Most severe condition was considered and the percentage of children with that score were calculated. Primary and permanent dentition analyzed separately. Results: CAST index – codes 0 in 54% in primary & 77% in permanent, CAST code 3 in 7% – primary & 5% – permanent, CAST codes 4, 5 in 21% – primary & 9% – permanent; CAST codes 6, 7: in 14% primary & 9% in permanent and lastly CAST– code 8 in 4%– primary and 0%– permanent dentition. Conclusions– None of the slum children had undergone any restorations even though treatment need was high.