[6][7] When he graduated, he began a career as a filmmaker, later winning a Golden Bear Award for an animated short, Hlavy, at the 1980 West Berlin Film Festival.

[9] Sís travelled to the United States in 1982 "to create an animated film based on Czechoslovakia's participation in the Olympics" that were upcoming in Los Angeles.

He has occasionally returned to filmmaking, producing commercials for Nickelodeon & PBS Kids, plus shorts for Sesame Street based on his book Madlenka.

He has received a Boston Globe–Horn Book Award four times: for Komodo (1993), A Small Tall Tale From the Far Far North (1994), Tibet Through The Red Box (1999), and The Wall: Growing Up Behind the Iron Curtain (2008).

Sís has won the Golden Bear Award at the 1980 Berlin International Film Festival for an animated short.