Background  The role of streptococcal infection in the initiation of guttate psoriasis is well-recognized. But the treatment results with oral erythromycin and phenoxymethylpenicillin are conflicting.

Objective  Our purpose was to evaluate the effectiveness of these antibiotics in the treatment of streptococcus associated guttate psoriasis comparing with a control group.

Methods  A total of 43 male patients with serologic evidence of a recent streptococcal infection were studied. Their mean age was 21 years (ranged between 19 and 23 years). These 43 patients were randomly allocated into three groups (no treatment group n = 15, erythromycin group n = 14, phenoxymethylpenicillin group n = 14). Both the treatment groups were treated for 14 d. All the groups were followed up for additional 4 weeks.

Results  There were no statistically significant improvement in any group and among the groups.

Conclusion  There was no statistically significant improvement in streptococcus associated guttate psoriasis with or without a course of oral penicillin or erythromycin.