Tooth‐coloured restorative materials are being used increasingly more often in Class II preparations in permanent teeth. Using a practice‐based study design, we aimed to assess the survival time of Class II restorations and to identify factors relevant to their longevity. Class II restorations (n = 4,030), consisting of resin composites (81.5%), compomers (12.7%), amalgams (4.6%), and glass‐ionomer cement restorations (1.2%), were placed in 1,873 patients with a median age of 15 yr. In total, 92.7% of restorations were placed due to primary caries and 5.8% were replacements. After an average follow‐up period of 4.6 yr, 61.6% of the restorations were successful, 11.2% had failed, and 27.2% were not available for evaluation (owing to patient drop‐out). The mean annual failure rate was 2.9% for resin‐composite restorations and 1.6% for amalgams. For resin‐composite restorations, secondary caries was the most common reason for replacement (73.9%), followed by loss (8.0%), fracture (5.3%), and marginal defects (2.4%). Multilevel Cox‐regression analyses identified young age of the patient, high previous caries experience, deep cavities, and saucer‐shaped preparation technique as predisposing to shorter longevity of resin‐composite restorations. One brand of resin composite had a shorter survival time than the others.