Aims: Ectopic eruption is a change in the normal path of eruption of a tooth. The aim of this study is to determine the prevalence of ectopic eruption of the permanent maxillary first molars in a Spanish subpopulation of 505 children, its distribution as regards age and gender, unilateral and bilateral occurrence and loss of space. Methods: Periapical and panoramic X-rays were taken of the patients, with six-monthly check-ups to evaluate development. A statistical analysis of the data was performed using the chi-square test (p lessthan 0.05, 95% C.I). Results: A prevalence of 6.7% was obtained being the most common age of presentation was seven years and bilateral occurrence (67.6% of cases) with no statistically significant differences as regards to the gender. Only 14 of the 505 explored patients required treatment for ectopic eruption. Conclusion: This study provides information regarding treatment needs and prevalence regarding molar ectopic eruption in a Spanish population. It is essential for professionals to be familiar with the diagnostic factors, clinical consequences and therapeutic options for ectopic eruption of permanent molars.