Frontal sinusitis, or inflamatory complications of sinusitis, may occur as a consequence of frontal craniotomy when the sinus has been entered during the craniotomy. This may happen particularly during surgery to treat an aneurysm or to excise a tumor in the sellar area. These complications may also occur if the sinus is entered during routine craniotomy when the sinus is high or asymmetrical, or during reduction of frontal bone fractures. This presentation describes the etiology of such inflammatory complications and describes the approach to treatment of such complications, as well as outlining their prevention.