The relationship between ulcerative colitis (UC) and pregnancy was studied in 83 cases (124 deliveries). The results were as follows: 1) In women with UC, there was no significant difference in fertility compared with the general population. 2) The existence of UC and treatment of UC during pregnant period had no significant adverse effects for the course of pregnancy. 3) In the 17 out of 36 pregnancies with inactive UC at the onset of pregnancy suffered relapses. Relapse rate in same patients in the pregnant period was significant higher than that in the non-pregnant period. 4) First attack of UC developing in 12 cases during pregnancies or the puerperium, the onset being commonly in the first trimester. UC developing during pregnancy was especially severe in other patients. We concluded that the relapse rate of UC is high during pregnant period, however, the course of pregnancy is not affected with UC.