BACKGROUND: Cancer of unknown primary (CUP) origin is cancer in which malignant cancer cells are in the body but the site of cancer where it began is unknown. Detailed incidence and time trends of these cancers, specific to various regions in India is needed. This paper aims to summarize and report the incidence of other and unknown (O&U) cancers across India in 27 population-based cancer registries (PBCRs) and to study the trends among these cancers using joinpoint regression analysis. METHODS: Data on the incidence of CUP were obtained from the published reports on 27 PBCRs of the National Cancer Registry Programme (NCRP) of the Indian Council of Medical Research (ICMR). A joinpoint regression model was used to analyze the long-term trends of incidence related to CUP based on published data from PBCRs between 1986 and 2014. Annual Percent Change (APC) in incidence rate was estimated for various registries. RESULTS: The northeast region had the highest age-adjusted rate (AAR) for both men (1.76-29.7) and women (1.99-14.68). Age-specific rate (ASR) for both men (39.8-855.7) and women (48.2-470.4) was highest in the northeast region. There is an increase in the incidence rate for all six major registries over the past decade with an exception of women in the Delhi Cancer Registry. There is a decline in incidence rate by 0.14 during 1990-2012 in the female population of the Delhi registry. CONCLUSION: The increasing incidence trends of CUP is a matter of concern for the healthcare professionals and researchers. There is a need for research and advanced and improved diagnostic tools for the improvement of the status of O&U cancers.