This preliminary report is based on a survey of the reasons for inserting 790 glass-ionomer cement, 2,609 resin composite, and 898 amalgam restorations in adults in general practice. Glass-ionomer materials were used about equally for the treatment of primary caries and for replacement of failed restorations, unlike resin composite and amalgam, which were most often used to replace failed restorations. Almost half of the 412 replaced glass-ionomer cement restorations were removed because of the clinical diagnosis of secondary (recurrent) caries, which was by far the most common reason for replacement of all three materials.