OBJECTIVE : Decamarcated hypomineralised lesions of enamel include those developmental defects that are related to MIH, HSPM or any other demarcated opacities of systemic origin. The present study's aims are to determine MIH/HSPM prevalence, caries lesion severity and their association in a sample of 6-12-year-old schoolchildren from Talca, Chile. METHODS : The sample (N = 577) was derived from selected primary schools in urban Talca. A full dental examination was performed at the school by one calibrated examiner. Socio-demographic data and caries experience (DMFT/dmft/merged ICDAS II and PUFA/pufa) were measured in primary and permanent dentitions. MIH/HSPM was assessed using a modified EAPD protocol. Binary and multilevel binary regression analyses were calculated. RESULTS : The prevalence of MIH/HSPM or other demarcated hypomineralised lesions was 24.4%. MIH and HSPM was 15.8% and 5%, respectively. The presence of HSPM predicted MIH (OR 3.7; 95% CI 1.65-8.15) when corrected by demographic factors. Of the children examined, 35% had no teeth with a score greater than ICDASII Code 0 and 26% had one or more severe carious lesions (Code C). Toothwise multilevel binary regression analyses demonstrated that teeth with MIH/HSPM (OR 3.70) from low-SES children (OR 1.93) had higher odds for carious lesions compared with defect-free teeth from high-SES participants. CONCLUSIONS : MIH/HSPM lesions were associated with carious lesion occurrence and increased disease severity. The prevalence of MIH and HSPM was similar to other reports. Increased awareness of MIH/HSPM in schools and primary health settings may help to identify children at risk early.