Cancer information services (CISs) are a valuable source of evidence-based information. Previous studies in the field of CISs often investigate only short periods of time. However, there is a need for long-term analyses to identify changes in the use of CISs.The purpose of this study was to analyze trends in the inquiries of patients and surrogate seekers to a CIS.We conducted a secondary data analysis of the inquiry records of the German CIS (Krebsinformationsdienst, KID) hosted by the German Cancer Research Center from 1992 until 2016 (N = 545,070). Trends in the number of inquiries were described using the whole sample, while the description of further characteristics is based on a sample (n = 55,046) of patients, their family members, and friends.The inquiries increased in the period examined (1992: 11,344 inquiries; 2016: 34,869 inquiries). Since 2005, a greater share of patients (between 52 and 60%) than surrogate seekers have been contacting the CIS. The mean age of both self-seeking and supported patients increased from under 55 years between 1992 and 2000 up to over 60 years in the year 2016. Breast cancer is at all times the most frequently inquired cancer type (patients: n = 11,319, 39%; surrogate seekers: n = 4173, 17%). Even after the implementation of e‑mail as an additional communication channel, the majority of inquirers still prefer contact by phone (between 80 and 98%).Changes in the utilization of a CIS over time are discussed against the background of structural changes, such as shifts in prevalence rates, family structures, or media environments.