The purpose of this study was to examine the effect of a stonnous fluoride pretreatment of dentin on the shear bond strength of a dentinal adhesive system with a composite resin restorative material. Dentinal specimens from 31 extracted human third molars were used in a matched-pair design. Statistical analysis of the data showed that pretreatment of dentin with the stannous fluoride solution significantly decreased the bond strength of the dentinal adhesive system (P = .0005). Clinicians should consider the negative effects of fluoride pretreatment of dentin when used in conjunction with dentinal adhesives and composite resin restorative materials.