A spokeswoman for Texas Woman's University says it has no details on Angelou's illness. A statement on the university's website says it hopes to reschedule the appearance for this semester.
Messages left at Angelou's Wake Forest University office in Winston-Salem, N.C., and the offices of her literary agent and her representative for speaking engagements were not returned. Her assistant did not immediately respond to an email.
The 83-year-old poet is hosting a radio special on the civil rights era airing on public radio stations across the U.S.
Last year, President Barack Obama presented Angelou with the Presidential Medal of Freedom. She also has received the Presidential Medal of Arts and the Lincoln Medal.