The purpose of this study was to investigate the reasons for placement and replacement of restorations provided to military personnel by all 34 dentists stationed in the four Atlantic provinces of Canada. All dentists who participated in this study are salaried. Over a period of 30 working days, each dentist recorded information on all restorations performed. Data were collected on dentists' year of graduation, patient age, treatment requirements, tooth number, restoration class, materials used and reasons for placement and replacement. All dentists used the same data collection form which was pilot tested. Information was collected on 2,280 restorations from 643 adults, 18 to 57 years of age. Of all restorations, 54.3% were placements and 45.7% were replacements. No difference in placement and replacement rates between amalgam and composites was reported. The major reason for placement was primary caries (90%). The major reasons for replacements were recurrent caries (40.0%), primary caries of interproximal surfaces (18.9%), and fractured restorations (12.3%). Of the 297 MOD restorations, 74.3% were replacements and of the 1,140 Class I + III + V restorations, 27.8% were replacements. This study showed that about half of the restorative work carried out were replacements. Caries is the primary reason for placement and replacement of restorations in adults.