The aim of this study was to determine whether the intensity of preoperative pain was a predictive factor for the prevalence and intensity of postoperative pain, considering demographic and clinical variables. The study involved́ 80 teeth with pulpal or periapical pathologies. Root canal treatment was performed in one or two sessions. Pain intensity was assessed using the visual analogue scale before treatment and then 6h, 12h, 24h, 48h, 72h and one week after root canal treatment. The sample consisted of 46 women and 34 men. This study showed́ that postoperative pain was statistically associated with female gender (p=0.05), tooth types (p=0.006), and its location on the mandibular arch (p=0.03). The main finding was that patients with a higher intensity of pre-operative pain had a higher incidence of post-operative pain (p<0.05). In the group of patients who had no pre-operative pain, 63% (17/27) of patients remained asymptomatic after root canal treatment, while only 7.4% (2/27) had severe post-operative pain with a significant difference (p<0.05). However, in the group with severe pre-operative pain, 100% of patients had post-operative pain, of which 75% (15/20) of patients had high levels of pain requiring analgesics.