Despite the simplicity, effectiveness, and safety of spinal anesthesia, arachnoiditis can occur as a complication. The cause of this is often unknown, especially since disposable spinal kits are now normally used. It is postulated that an untoward reaction to the anesthesia or chemical contamination was the cause of arachnoiditis in our patient. We also outline the use of MRI in the diagnosis of arachnoiditis. This mode of investigation is often sufficient to establish the diagnosis. When necessary, it can be augmented by myelography and CT.