To determine the prevalence of nonfluoride enamel hypomineralization in the permanent first molars, we examined 488 7- to 13-year-old children. We further examined the impact of such defects on the treatment need by evaluating the number of caries lesions, restorations and extractions of the target teeth. Nonfluoride hypomineralization(s) were seen in 94 children (19.3%). The severity of defects varied from mild lesions with local color change to more severe ones where the hypomineralized tissue had been replaced by a restoration or the tooth had been extracted. Further examination of 65 children with nonfluoride hypomineralization showed that the defects had significantly increased the treatment need of the target teeth compared with the age- and sex-matched controls (p<0.001). Consequently, also the DMFT index of the whole dentition was higher in the children with hypomineralizations than in the controls (p<0.05). The results indicate that nonfluoride hypomineralizations have a significant impact on treatment need in the present child population with low caries activity.