Background: The aim of this study was to analyze the effects of erbium-doped:yttrium, aluminum, and garnet (Er:YAG) laser and ultrasonic treatment on fibroblast attachment to periodontally diseased root surfaces. Methods: Thirty single-rooted human periodontally involved teeth were included in this study. A total of 60 specimens were obtained from all selected teeth and were randomly assigned to the following three groups: group A, untreated control group; group B, ultrasonic group; and group C, Er:YAG laser at 160 m J/pulse at 10 Hz group. All of the specimens were incubated in petri dishes with fibroblast suspension and observed by scanning electron microscopy. Results: Laser-treated specimens showed a significantly higher cell density number, with a mean ± SD of 3,720 ± 316 cells/mm². The ultrasonically treated group showed a lower cell density number, with a mean ± SD of 658 ± 140 cells/ mm². The untreated control group showed the lowest cell density number, with a mean ± SD of 130 ± 80 cells/mm². Differences between all groups were significant (P <0.0001 ). Conclusion: The results of the study indicate that untreated control surfaces and ultrasonically treated surfaces exhibited a significantly lower number of attached cells compared to laser-treated specimens, which showed a significantly higher cell density number. [ABSTRACT FROM AUTHOR]