Background: The objectives of this study were to: 1) test hypotheses that behavioral factors, baseline clinical status, and incident tooth loss are significantly associated with attachment loss incidence (ALI) and 2) quantify the effect of incident tooth loss on conclusions made about ALI. Methods: The Florida Dental Care Study was a prospective study of persons ≥45 years old. In-person interviews and examinations were conducted at baseline and 48 months, with telephone interviews in between. Results: Of 560 persons with baseline and 48-month examinations, 22% of persons and 1.8% of teeth had ALI. This was highest among persons with no dental visit during follow-up (person-level incidence of 46%; 5.0% tooth-level incidence). Statistically significant covariates in a multivariable regression of ALI were: losing a tooth due to periodontal reasons after baseline, but before the 48-month examination; not receiving a dental cleaning; and baseline factors (worst attachment level of ≥7 mm, not flossing, a molar tooth, current smoker). Conclusions: A substantial percentage of persons experienced ALI. Baseline attachment level and behavioral factors were significantly associated with ALI. Persons with incident tooth loss were also at increased risk for ALI, and teeth lost during follow-up had worse baseline attachment level. Had these teeth not been lost before the final examination, the ALI estimate could only have been higher. These findings demonstrate that those at greatest risk for ALI are least likely to enter the dental care system, and among those who do, one health outcome (tooth loss) can affect conclusions made about the incidence of another (ALI).