The recurring chromosomal 1;19 translocation in acute lymphoblastic leukemia (ALL) occurs in balanced t(1;19) (q23;p13) and unbalanced, -19, +der(19)t(1;19)(q23;p13) forms. The clinical features and outcome were compared for 30 patients with the t(1;19) and 36 patients with the der(19) forms. These were 45 children (less than 1-14 years) and 21 adults (15-54 years) (median age 9.0 years), 41 females, 25 males, with median white blood count (WBC) 20.9 x 10(9)/1. Patients were classified by karyotype thus: t(1;19) 11 cases; t(1;19) with additional change (+A) 19 cases; der(19) 17 cases; and der(19) +A, 19 cases. Non-random additional structural abnormalities included involvement of 1q, 6q, i(7q), i(9q), 9p, and 13q. The only significant difference in clinical or blast cell features between patients with the t(1;19) and the der(19) was the greater age of adults with t(1;19) (p less than 0.05). Projected median event-free survival and survival of all cases together was 22 months and greater than 112 months respectively. Neither age nor WBC contributed significantly to prognosis. For patients at all ages, prognosis of der(19) was better than t(1;19). This was statistically significant for event-free and overall survival in childhood (p = 0.02 and p = 0.01 respectively) and was independent of age (p = 0.04 and p = 0.008 respectively) and WBC (p = 0.03 and p = 0.04 respectively). Future studies should examine separately the outcome for patients with the balanced and unbalanced forms of the t(1;19).