Three patients affected with nail psoriasis of the fingers in whom the use of topical 5-fluorouracil (5-FU) led to yellow nail discoloration are reported. Based on the fact that yellow nails are associated with a slow nail growth rate, nail growth in these patients ('bad responders') and in two individuals, both affected with psoriasis, who had previously responded favorably ('good responders') to topical 5-FU for their nail condition were compared. The results of nail growth measurement revealed that mean longitudinal growth in 'bad responders' was lower than that in 'good responders'. In conclusion, although topical application of 5-FU is an effective treatment for nail psoriasis, we suggest its use in those patients in whom nail growth is not significantly impaired. For that reason an observational period to evaluate nail growth prior to treatment with topical 5-FU would be an adequate means of patient recruitment.