Slijkhuis began his international sports career shortly after World War II, having competed nationally since 1939.

Slijkhuis' achievements were overshadowed, however, by the performances of compatriot Fanny Blankers-Koen, who won four gold medals at the same Olympics.

During his career Willem Slijkhuis didn't just run almost everywhere in Europe, but also in New Zealand, South Africa and the United States.

Owing to his stubborn behaviour Slijkhuis sometimes clashed with officials of the Dutch Athletics Federation, who he accused of outrageous interference.

[1] Slijkhuis, who won eleven national titles – including eight in the men's 5000 metres – on track, seven in Cross country running and set thirty Dutch records, ended his career in 1954 due to injuries.