Purpose: To analyze the clinical, microbiologic, and host response characteristics (interleukins 1ß and 6) in the peri-implant sulcus fluid (PISF) of patients with healthy dental implants and with peri-implant mucositis. Materials and Methods: Clinical parameters (modified Gingival Index [mGI], modified Plaque Index [mPI], probing pocket depth [PPD], and absence or presence of radiologic bone loss) were recorded, and PISF samples were obtained from peri-implant sites showing mucositis as well as healthy sites. The periodontopathogenic bacteria Tannerella forsythia (Tf), Treponema denticola (Td), and Porphyromonas gingivalis (Pg) were evaluated, together with the total bacterial load (TBL) and the interleukin (IL) 1ß and IL-6 values. Results: The study population consisted of 34 individuals, and 77 dental implants were evaluated during the study (23 mucositis and 54 healthy peri-implant sites). The mGI, mPI, and PPD scores of the peri-implant mucositis group were significantly greater than in the healthy group. No differences in detection frequency were found for putative periodontal pathogens and TBL between the healthy peri-implant sites and mucositis sites. The mucositis group showed a significantly greater expression of IL-6 than the healthy group (P .05). Although IL-1ß was increased in the mucositis group, there was no statistically significant difference versus the healthy implant group. Conclusions: An analysis was made of the clinical, microbiologic, and host response characteristics in implants with peri-implant mucositis, establishing comparisons with healthy implants. In the patients studied, bacterial plaque induced an inflammatory response that can lead to the development of peri-implant mucositis. Adequate plaque control is therefore able to increase peri-implant health, avoiding the risk of future complications. No specific association to the studied bacterial species was established.