Background. The COVID-19 pandemic has disrupted the provision and use of healthcare services throughout the world. In Slovenia, an epidemic was officially declared between mid-March and mid-May 2020. Although all non-essential health care services were put on hold by government decree, oncological services were listed as an exception. Nevertheless, as cancer control depends also on other health services and additionally major changes in people’s behaviour likely occurred, we aimed to analyse whether cancer diagnosis and management were affected during the COVID-19 epidemic in Slovenia. Methods. We analysed routine data for the period November 2019 through May 2020 from three sources: (1) from the Slovenian Cancer Registry we analysed data on pathohistological and clinical practice cancer notifications from two major cancer centres in Ljubljana and Maribor / (2) from the e-referral system we analysed data on all referrals in Slovenia issued for oncological services, stratified by type of referral / and (3) from the administrative data of the Institute of Oncology Ljubljana we analysed data on outpatient visits by type as well as on diagnostic imaging performed. Results. Compared to the November 2019 – February 2020 average, the decrease in April 2020 was about 43% and 29% for pathohistological and clinical cancer notifications / 33%, 46% and 85% for first, control and genetic counselling referrals / 19% (53%), 43% (72%) and 20% (21%) for first (and control) outpatient visits at the radiotherapy, surgery and medical oncology sectors at the Institute of Oncology Ljubljana, and 48%, 76%, and 42% for X-rays, mammograms and ultrasounds performed at the Institute, respectively. The number of CT and MRI scans performed was not affected. Conclusions. Significant drops in first referrals for oncological services, first visits and imaging studies performed at the Institute, as well as cancer notifications in April 2020 point to a possibility of a delayed cancer diagnosis for some patients during the first surge of SARS-CoV-2 cases in Slovenia. The reasons for the delay cannot be ascertained with certainty and could be linked to health-seeking behaviour of the patients, the beliefs and practices of doctors and/ or the health system management during the epidemic. Drops in control referrals and control visits were expected and are most likely due to the Institute of Oncology Ljubljana postponing non-essential follow-ups through May 2020.