BACKGROUND AND OBJECTIVES: We explored the predictive value on therapy outcome of an early evaluation of treatment response by 18F-fluorodeoxyglucose position emission tomography (18F-FDG-PET) scan performed after two courses of conventional standard-dose chemotherapy in advanced-stage Hodgkin's disease. DESIGN AND METHODS: One hundred and eight patients with newly-diagnosed Hodgkin's disease in stage IIA with adverse prognostic factors, or in stage IIB through IVB, were re-staged with FDG-PET after two cycles of ABVD (PET-2). The end-point of the study was the predictive value of PET-2 on 2-year progression-free survival and 2-year failure-free survival. No treatment variation based only on PET-2 results was allowed. RESULTS: Eighty-eight patients attained complete remission (CR) while 20 showed disease progression during therapy or within 6 months after having reached CR; one patient relapsed. PET-2 was positive in 20 patients: 17 progressed during therapy, one relapsed and two remained in CR. By contrast, 85/88 (97%) patients with a negative PET-2 remained in CR; three progressed or relapsed early after the end of the chemotherapy. Thus, the positive predictive value of a PET-2 was 90% and the negative predictive value was 97%. The sensitivity, specificity and overall accuracy of PET-2 were 86%, 98% and 95%, respectively. The 2-year probability of failure-free survival for PET-2 negative and for PET-2 positive patients was 96% and 6%, respectively (log rank test = 116.7, p