Progressive transformation of germinal centers (PTGC) occurs focally in reactive lymph nodes, and has been reported with increased frequency in patients with nodular lymphocyte predominance Hodgkin's disease (NLPHD). It has been suggested that patients with lymph node biopsy samples showing PTGC are at increased risk for the development of NLPHD, and that Hodgkin's disease may evolve from PTGC. We report five young men (ages 14-24 years, mean 18) with prominent lymphadenopathy and florid PTGC, in whom careful examination and follow-up showed no progression to Hodgkin's disease. Three patients developed adenopathy that involved several node groups and two had localized adenopathy. Cervical (2), inguinal (2) and axillary (1) nodes ranging from 3 to 4 cm were excised. The number of progressively transformed germinal centers (PTGCs) ranged from 10 to 123 per specimen (mean 67); single sections contained nine to 29 PTGCs (mean 19). In three cases the nodal architecture was significantly distorted, suggestive of NLPHD, but Reed-Sternberg cells were absent. Follow-up is available for all patients (all untreated): three patients had persistent adenopathy 1 year 4 months to 10 years after diagnosis. Results of repeat biopsy in two patients (2 and 3 years after diagnosis) showed florid PTGC with no evidence of Hodgkin's disease. One of these patients had one subsequent biopsy 8 years after presentation; results showed only rare PTGCs. The fourth and fifth patients, who had presented with isolated adenopathy, were free of recurrent adenopathy at 2 and 5 years. These cases suggest a syndrome of lymphoid hyperplasia with florid PTGC in adolescent boys and young men. Although adenopathy can persist, there has been no progression to Hodgkin's disease. Recognition of this syndrome is important to avoid overdiagnosis of LPHD. Close follow-up of these patients will be necessary to evaluate the relationship of this disorder to NLPHD.