This study involved 108 patients (age 38-82 years) rehabilitated with overdentures in the lower jaw supported by 2 endosseous screw-shaped implants. At each follow-up visit, the clinical attachment level (PAL) around the implants was assessed with a Merrit-B probe or a constant force electronic probe, Peri-probe, and biannually parallel long-cone radiographs were taken to locate the marginal bone level. These data were used to examine the relationship between bone and attachment level estimations around implants. As a mean, bone level and PAL, for mesial and distal sites, was 0.67 and 0.61 for the Merrit-B probe, and 0.76 and 0.65, respectively for the Peri-probe. The highest correlations were obtained for sites with a healthy gingiva or in absence of intra-bony craters. Duplicate PAL registrations showed a standard deviation for the intra-examiner variability of 2.37 (Peri-probe) or 0.40 mm (Merrit-B probe) with more than 90% of the variation within 0.5 mm. The mean difference in PAL between Merrit-B probe or Peri-probe was 0.05 mm. It was concluded that the clinical attachment level determination is a reliable indicator for bone level around implants with a moderate healthy gingiva.