The role of chest irradiation in the treatment of small cell lung cancer remains controversial. Two meta-analyses have shown a significant improvement of survival when this therapy is associated to chemotherapy but the controlled studies individually lead to contradictory conclusions. We have performed qualitative and quantitative evaluation of the literature on this topic in order to try to clarify this problem. On 15 published trials, 8 only give sufficient data allowing a meta-analysis. This does not show that chest irradiation improves statistically significantly survival in comparison to chemotherapy alone (odds ratio = 0.82; 95% CI: 0.63-1.07). The qualitative evaluation has been performed with the Chalmers and ELCWP scales. The scores obtained by both methods are highly correlated. There is no significant difference between the scores obtained by studies showing a survival improvement with irradiation or by negative studies. Very few trials report important criteria like definition of the primary end-point or the a priori estimate of the population size, attesting important methodological deficiencies. In conclusion, the quantitative aggregation of studies seems difficult to interpret because of the non optimal quality of the studies.