Abstract Background TNM staging of cancer is used to establish the treatment and prognosis for cancer patients, and also allows the assessment of screening programmes and hospital performance. Collection of staging data is becoming a cornerstone for cancer registries. The objective of the study was to assess the completeness of T, N, M and stage grouping registration for all cancers in the Mallorca Cancer Registry in 2006–2008 and to explore differences in T, N, M and stage grouping completeness by site, gender, age and type of hospital. Methods All invasive cancer cases during the period 2006–2008 were selected. DCO, as well as children’s cancers, CNS, unknown primary tumours and some haematological cases were excluded. T, N, M and stage grouping were collected separately and followed UICC (International Union Against Cancer) 7th edition guidelines. For T and N, we registered whether they were pathological or clinical. Results Ten thousand two hundred fifty-seven cases were registered. After exclusions, the study was performed with 9283 cases; 39.4 % of whom were women and 60.6 % were men. T was obtained in 48.6 % cases, N in 36.5 %, M in 40 % and stage in 37.9 %. T and N were pathological in 71 % of cases. Stage completeness exceeded 50 % in lung, colon, ovary and oesophagus, although T also exceeded 50 % at other sites, including rectum, larynx, colon, breast, bladder and melanoma. No differences were found in TNM or stage completeness by gender. Completeness was lower in younger and older patients, and in cases diagnosed in private clinics. Conclusions T, N, M and stage grouping data collection in population-based cancer registries is feasible and desirable.