The aim of this study was to compare the retention rate of a glass ionomer cement formulated for fissure sealing with two resin-based sealants, 208 occlusal fissures of permanent molars and premolars were sealed with either Fuji III, Delton or Concise WS by four dentists. Clinical assessments and a replica scoring technique were used to register the performance of the sealants at baseline, after 6-12 months, and then yearly up to 5 yr. As judged clinically, 61% of the glass ionomer sealants were lost within 6-12 months and 84% after 30-36 months. Although total loss was recorded clinically for the majority of the glass ionomer sealants, some retained sealant was observed in the tooth replicas in 93% of them. The clinical evaluation of the resin-based sealants showed an average complete retention rate of 90% after 4.5-5 yr. The corresponding figure with the replica technique was 58%. Caries was recorded in 5% of the resin-based and in none of the glass ionomer sealed surfaces.