The aim of this study was to improve the transdermal permeation of sodium diclofenac. Permeation studies were carried out in vitro using human skin (0.4 mm thick) from plastic surgery as a membrane. Four liquid formulations of 1% (w/w) sodium diclofenac were assayed: three ternary solvent systems (M4, M5, M6) and one microemulsion (M3). A 1% (w/w) solution of sodium diclofenac and a commercially available semisolid preparation were tested as reference formulations. The following permeation parameters for diclofenac were assessed: permeability coefficient, flux and drug permeated and retained in the skin at 24 h. The highest values of these parameters were obtained with formula M4, which contains transcutol 59.2%, oleic acid 14.9% and d-limonene 5% (w/w) as permeation enhancers. The anti-inflammatory activity of this formula was compared with that of the semisolid preparation on carrageenan-induced paw edema in rats. As expected from in vitro results, the M4 diclofenac delivery system showed higher activity than the semisolid preparation, both when applied locally (to the inflammation area) and when applied systemically (to the back). Neither treatment irritated the skin when tested on rabbits in a 72-h trial. These results suggest that topical delivery of sodium diclofenac with an absorption enhancer such as a mixture of oleic acid and d-limonene (M4) may be an effective medication for both dermal and subdermal injuries.