Abstract A parallel examination of interview data and register data provides a more holistic overall picture of social security needs and use than any one type of data alone. In our study, we aimed to build a comprehensive understanding of the benefit and service needs of parents whose child is diagnosed with cancer. Conducting solely interviews would have provided subjective perceptions of individuals in the midst of a challenging life situation, but the data would have lacked information of the participants’ documented use of social security benefits and services. On the other hand, utilizing solely register data, would have provided an objective overview of actual service use. However, register data alone would not have shed light on whether the benefits and services received were sufficient from the recipients’ point of view. In our study, parents’ interviews and their register data from the Social Insurance Institution of Finland (Kela) offered complementary perspectives on the same life situation. Parents’ interviews provided information on support needs, service experiences as well as service deficits. The same families’ register data was used with their permission producing exact data on the insurance benefits and services that the family had applied for and received. The interviews were analysed as chronologically progressing narratives while the data received from Kela was depicted on timelines. When conjoined, the interview and register data formed a comprehensive picture of the benefit and service needs and use of families, whose child had cancer. In addition, this kind of triangulation revealed service deficits that were acknowledged by the interviewees and identified also through the register data. We argue, that combining subjective interviews together with institutional register data allow researchers to identify issues in the service system, which require improvements from the recipients’ and the system’s perspective. Key messages • The use of multiple types of data allows researchers to construct a holistic understanding of individuals’ social security needs and use. • Combining interview and register data allows researchers to identify issues in the service system, which require improvements.