Three hundred and thirty seven truck drivers, in transit from Mombasa to destinations within east and central Africa were interviewed on their knowledge on AIDS and sex practices using a pre-defined questionnaire. Nearly all of them, 99% (3.7/321), had heard of AIDS through mass media and from friends. When asked for a definition of AIDS, 87% (336/485 responses) described it as a sexually transmitted disease (STD) which causes body wasting and death. The majority were aware of the correct risk reducing behaviours: 76% (228/300) knew that use of condoms can prevent the transmission/acquisition of STDs but only 32% (90/295) had ever used them. This was in spite of the fact that 61% (226/309) admitted to visiting prostitutes. Various reasons were given for not using condoms. About 32% (34/188) claimed that they did not sleep with prostitutes while 18% (34/188) did not see the need for using condoms. Condoms were unavailable to another 18% (34/188). The data obtained show a clear lack of correlation between the correct knowledge of AIDS and application in the prevention of acquisition and transmission of STD.