We systematically reviewed the evidence concerning the ability of five systemic treatments to induce remission in patients with severe psoriasis: ultraviolet B (UVB), photochemotherapy (PUVA), methotrexate (MTX), retinoids (RET) and cyclosporin A (CYA). An elaborate literature search was performed, the validity of studies was assessed, and data were analysed. In total, 89, 193, 101, 155 and 127 studies (n = 665) concerning UVB, PUVA, MTX, RET and CYA were found. The exclusion rate was high, mainly because of concomitant antipsoriatic therapy, outdated dosages or inadequate documentation. No study on MTX could be included. A total of 129 patient series was included in the analysis, reporting on 13,677 patients. Study size-weighted averages of the proportions of patients with clearance and good, moderate and poor response (defined, respectively, as 95-100%, 75-100%, 50-75% and < 50% reduction in the outcome measurements as compared with baseline) were calculated. PUVA therapy was associated with the highest average proportion of patients with clearance (70%), and the highest proportion of patients with good response (83%), followed by UVB (68%) and CYA (64%). Incidence of side-effects per week was highest in the RET group and lowest in the phototherapy groups. This review may provide a basis for the development of guidelines for the treatment of psoriasis. Trials comparing oral modalities applied according to currently accepted standards should also be carried out.