Abstract Background One of the long-term effects in childhood cancer survivors (CCS) is the development of second cancers. In a cohort of CCS, this study describes how second cancers were presented, the way they were diagnosed, and the knowledge CCS had about their increased risk to develop a second cancer. Patients and methods Selected participants were all adult five-year CCS (n = 1275) who were treated at the University Medical Center Groningen since 1965. Of these, 84 (6.6%) had developed a second cancer, of which 27 had died. The 57 survivors were asked to participate in a telephone interview. Results Of the 57 CCS, 35 (61%) participated. Together they had developed 45 second cancers. Most participants (97%) were seen at the long-term follow-up clinic. Of all second cancers, 89% caused symptoms. Of all second cancers, the majority (56%) were first presented at the general practitioner's (GP's) office and 20% at follow-up testing. Of these CCS, only 28% were aware of their increased risk of developing a second cancer. Conclusions It is important to inform CCS continuously regarding their increased risk, as a relatively small percentage are aware of this. Since most of these patients first reported their symptoms to the GP, all GPs should be aware of this increased risk, in particular because this concerns cancer at a younger age than normally expected. A survivor care plan might be an effective way of communication with both CCS and GPs.