We studied patient-derived variables to identify individuals at risk for future clinical attachment loss (CAL). Seventy-five patients with chronic adult periodontitis were followed for 6 months and clinical and epidemiological parameters collected at baseline were related to CAL. Clinical parameters were obtained from 6 sites per tooth and whole-mouth averages were calculated. Epidemiologic parameters were obtained by questionnaire and interview. After the baseline examination, patients were treated with root planing and scaling. Thirty-one patients (41.3%) demonstrated greater than or equal to 1 site with CAL of greater than or equal to 2.5 mm, while 16 patients (21.3%) demonstrated CAL at greater than or equal to 2 sites. Epidemiological factors such as gender, health status, marital status, education, and occupation were not associated with CAL. In contrast, baseline mean attachment level, age, baseline mean probing depth, baseline mean recession, percentage of sites exhibiting bleeding on probing, and the number of missing teeth were related to CAL. Using logistic modelling, we found that baseline attachment level was the primary risk indicator for post-treatment CAL. Nineteen percent of the patients with baseline attachment levels less than 4.0 mm, 50% of the patients with 4.0 to 4.9 mm, and 85% (P less than .005) of the patients with greater than or equal to 5.0 mm exhibited CAL. The age of the patient was also a major risk indicator for CAL, and was independent of baseline attachment levels. Eighty-nine percent of the 60 to 69 year old patients demonstrated CAL, compared to only 35% of patients between the ages of 30 and 59 (P less than or equal to .005).(ABSTRACT TRUNCATED AT 250 WORDS)