BACKGROUND: It has been suggested that addition of a basal infusion (BI) to patient-controlled analgesia (PCA) improves the continuity of analgesia for post-operative pain, by maintaining a minimum effective blood concentration of opioids between PCA demands. The aim of this study was to determine whether the addition of a BI to PCA using fentanyl would lead to improved pain control and patient satisfaction without increasing the side effects. METHODS: Seventy three patients, ASA class I or II, aged 22 - 72 years, following an orthopedic surgery under general anesthesia were studied. Patients were randomly allocated into two groups as follows: PCA group (n = 37), fentanyl 20 microgram demand dose with a lockout time of 6 min; PCA + BI group (n = 36), addition of fentanyl 20 microgram/h as a BI in the same regimen as the PCA group. RESULTS: Pain scores, patient satisfaction, sedation, and incidence of side effects were similar between the two groups. However, total consumption of fentanyl during the first 24 h after surgery was significantly increased in the PCA + BI group compared with those in the PCA group (1114 +/- 334 microgram vs. 841 +/- 409 microgram, P < 0.05). CONCLUSIONS: Despite the increased fentanyl consumption, the pain scores and patient satisfaction were not improved in the PCA + BI group. Addition of a BI at 20 microgram /h of fentanyl did not confer any advantage over a PCA alone and is not recommended when fentanyl PCA is used after orthopedic surgery.