This study investigated the association between several demographic, socio-economic, behavioural and clinical variables on caries activity. One hundred and two patients were randomly retrieved from the files of the Operative Dentistry Clinic (UFPel-Brazil). The patients gave written consent to participate in the study. They were interviewed reporting demographic (sex and age), socio-economic data (income, educaional level) and oral health behaviours (tooth-brushing frequency, dental floss usage and snacks frequency). Intraoral examination was performed to investigate the clinical variables (presence and quality of biofilm, DMFT and modified DMFT index and bleeding points). Patients were divided between caries-active (n=51) and caries-inactive (n=51), according to the presence of white spot lesions and/or active cavity lesions. Statistical analysis was carried tout using Chi-square or Fischer's exact test, with the confidence level at 95%. Results demonstrated that several conditions (younger subjects, lower educational or income levels, lower tooth-brushing frequency, higher snacks frequency, adherent biofilm, presence of bleeding points and higher modified DMFT index) were associated with caries activity in the studied population. Within the limitations of the experimental design, and considering the population under investigation, it was verified that demographic (age), socio-economic (income and educational levels), behavioural (tooth brushing and snacks frequencies) and clinical (modified DMFT index, presence and quality of biofilm, and bleeding points) variables were associated with caries-active patients. Keywords: caries activity, clinical trials, dental biofilm, oral health