Background: Since 1988 we have used mantle irradiation alone for patients with CSI or II HD with low probability of abdominal involvement at laparotomy (i.e.: patients with NS or LP histology, no B symptoms, and a No. of involved sites ≤4; Cancer 1989, 63: 1799-803) and no more than one of the negative prognostic factors (male sex, age >40, ESR > 40, No. of involved sites >2, or bulky palpable nodes) identified in another analysis.Patients and Methods: Between July 1988 and December 1994 we treated 27 previously untreated adult patients with CS I or II HD without bulky mediastinal disease who had a predicted probability of abdominal involvement ≤10% and no more than one negative prognostic factor. Twenty-six patients received RT to mantle field only and were considered evaluable and one patient that received subtotal nodal RT was excluded. Eight patients had CS I and 18 had CS II HD, 21 patients had NS and 5 had LP histology. Negative prognostic factors were male sex in 10 patients, ESR > 40 in two, and No. of sites involved >2 in 4 patients Results: With a median follow-up of 62 months, 20 patients remain with no evidence of relapse and 6 have relapsed. The 5-year DFS was 76% and the 5-y survival was 100%. The 5-y DFS was 88% in patients with CS I and 71% in patients with CS II. In patients with CS II disease, the risk of relapse increased as the predicted probability of abdominal involvement increased (p = 0.06; Logrank test for trend).Conclusions: The group of patients with CS I HD defined above can be spared the morbidity of laparotomy and subdiaphragmatic RT and still have high probability of DFS. Further study is necessary to establish what subgroup of CS II patients would be suitable for this approach but our data suggest that the predicted probability of abdominal involvement could be useful to identify that subgroup.