Purpose: The purpose of this study was to compare pain, efficacy and postoperative complications of anesthesia in first primary mandibular molars anesthetized with either intraligamentary (IL) or supraperiosteal (SP) anesthesia using a computer-controlled delivery system (CCDS). Study design: This randomized, controlled crossover, blind clinical trial was conducted with 90 children requiring bilateral extraction, pulpotomy or restorative treatment of first mandibular primary molars. A CCDS was used to deliver IL anesthesia to 1 deciduous tooth and SP anesthesia to the contralateral tooth in each patient. Severity of pain and efficacy of anesthesia during the treatments were evaluated using the Wong-Baker Faces Pain Rating Scale (PRS) and comfort and side effects were assessed using post-injection and post-treatment questionnaires. Data were analyzed using chi(2) and Mann-Whitney U tests. Results: According to PRS scores, pain levels during extraction were significantly higher with IL when compared to SP Patients reported significantly less pain during needle insertion with SP when compared to IL; however, rates of postoperative complications were significantly higher with SP when compared to IL. Conclusions: CCDS-administered IL anesthesia and SP anesthesia were similarly effective when used during restorative treatment and pulpotomy of primary mandibular molars; however; SP was more effective than IL when used during extraction procedures.