Objectives: The aim of this study was to clinically detect the immediate effect of root instrumentation with curettes and ultrasonic scalers on clinical attachment level. Material and Methods: Twelve subjects with moderate chronic periodontitis, presenting probing depths of 3.5–6.5 mm on anterior teeth, upper and/or lower, were selected. Teeth were randomly assigned to one of the following groups: US group – scaled with an ultrasonic scaler; and CC group – scaled and planed with 5–6 Gracey curettes. The selected teeth were probed with a computerized electronic probe, guided by an occlusal stent and subjected to scaling and root planing. Immediately following instrumentation, teeth were probed again. The difference between relative attachment level (RAL) immediately before and after instrumentation was considered trauma from instrumentation. Results: Intra‐group analysis revealed statistically significant differences between RAL immediately before and after instrumentation in both groups (0.77±0.51 for US group; and 0.73±0.41 for CC group, p<0.0001). However, inter‐group analysis did not show statistically significant difference in trauma from instrumentation caused by the two different instruments (p=0.816). Conclusions: Within the limits of this study, it was concluded that root instrumentation causes a mean immediate attachment loss of 0.75 mm, and that instrumentation with either curettes or ultrasonic scalers do not seem to reduce significantly the trauma from of instrumentation produced.