Difficult-to-treat dermatophytosis is an emerging public health problem in Sri Lanka. Safe, effective and affordable treatment is needed to solve this problem. Therefore this study has assessed the effectiveness and safety of modified Whitfield ointment applied twice daily with oral griseofulvin 500 mg daily given over 8 weeks in patients with difficult-to-treat dermatophytosis. A randomized, double-blind, within-patient-placebo-controlled trial was conducted in patients with clinico- mycologically (history, physical examination, direct light microscopy examination of scales in potassium hydroxide mount) confirmed difficult-to-treat dermatophytosis. Lesions were randomized to receive modified Whitfield ointment (5% benzoic acid and 5% salicylic acid) or emulsifying ointment. All patients were given oral griseofulvin 500mg once daily. The outcome measures were clinical assessment of disease severity, the total surface area of the lesions and the patient's perception of the disease severity at baseline and every two weeks up to a maximum of 8 weeks. Thirty patients completed the study. At two weeks, there was a statistically significant improvement in modified Whitfield ointment arm in the clinical assessment of disease severity and the patients' perception. There was a 7.59% reduction in the surface area of lesions in modified Whitfield ointment arm and a 5.83% increase in the surface area of lesions in the emulsifying ointment arm at two weeks. The difference between the two arms in surface area changes was not statistically significant (p = 0.107, df = 29). A combination of modified Whitfield ointment with griseofulvin is significantly effective, safe and affordable option for treating difficult-to-treat dermatophytosis in the tropics.