Objective: This in vitro investigation aimed to determine the radiopacity of eight recently introduced flowable restorative resin composites and to compare their radiodensities to those of enamel, dentin, and a widely used composite marketed for universal application in anterior and posterior teeth. Method and materials: A total of 45 composite specimens were fabricated in cylindrical molds and exposed to a curing light for 120 seconds. Two methods were used to determine radiopacity: a transmission densitometer and a computer-assisted densitometric image analysis station. Results: Of the eight flowable resin composites tested, only three exhibited a radiopacity equal to or greater than that of enamel, a widely followed guideline for clinicians' diagnostic ability. The radiopacity of the remaining five materials was not statistically significantly greater than that of dentin. Conclusion: The level of radiopacity of the tested flowable composites was variable; those with low radiodensity should be avoided in Class II restorations, where a clear determination of recurrent caries by the examining clinicians could be compromised.