In 2009, the five most common cancer types in Taiwan were lung cancer, liver cancer, colorectal cancer, gastric cancer, and female Torin 1 breast cancer. Since 2010, oral cancer replaced gastric cancer as the fourth most common cancer type. These high incidence and mortality rates result in major medical expenditures and large socioeconomic impacts on patients, their families, and the society as a whole. Analyses of cancer-related costs are usually performed in three phases to reflect clinical and cost-related dynamics: initial phase, continuing phase and final phase. Previous studies of cancer care costs have shown that a sizeable portion of cancer care costs are incurred in the initial phase. Taiwan studies of cancer costs have been limited to specific expenditures or to specific disease phases. Some Taiwan studies have also analyzed the cost effectiveness of specific cancer screening programs designed for early detection of cancers. Such studies analyze macroeconomic data related to specific procedures. Therefore, the purpose of this study was to estimate cost trends in initial cancer care during 1996–2007. The analysis focus on patients diagnosed with breast, colorectal, liver, lung, or gastric cancer since these cancers comprise approximately 60% of all cancers in the nationwide population. Despite the high cost of initial cancer care, data for specific categories of cancer-related expenditures, especially costs of specific services, are limited. This study analyzed cost trends in specific healthcare services as well as overall cost trends. We hypothesized that the increases in initial care costs reflect both increased rates of treatment for cancer patients and increased costs of specific therapies. To the best of our knowledge, this population-based study is the first to assess nationwide trends in the cost of initial cancer care in Taiwan. As health-care costs continue to increase, understanding cost trends in health care and identifying contributing factors in increased treatment costs will be important for planning for future health-care costs and for prioritizing and allocating medical resources. This study revealed significant increases in the mean total cost incurred by the NHI for treating patients with lung, liver, colorectal, breast, or gastric cancers in the initial period after diagnosis. Since these trend estimates provide working assumptions about health service costs and dissemination, health investigators can use these baseline data to model complex cost structures of specific emergency technologies and medical practices. This Taiwan study revealed increases in the mean total cost of initial treatment for five specific cancers during 1996–2007. This result, which is consistent with previous studies, may be due to an aging trend in the overall population and to an increased survival rate for these specific cancers as a result of improvements in health-care treatment models, medical utilization, hightechnology equipment, and payment systems. In a review of cancer studies performed in the United States, Warren et al. reported statistically significant increases in initial cancer care costs.