BackgroundThe concept of ‘complexity’ is widely used by healthcare professionals in patient care. However, it is not completely understood. The inappropriate use and incorrect understanding of complexity lead to ambiguity for hospital-based physiotherapists in dealing with complex patients and work situations.ObjectivesTo develop an understanding of complexity for hospital-based physiotherapy from the perspective of physiotherapists themselves.DesignA grounded theory study was conducted using data from face-to-face, semi-structured interviews with purposive sampled hospital-based physiotherapists. The sampling was used to incorporate variety in hospital work experience, field of expertise and gender. The interviews were conducted in three different types of Dutch hospitals. A conceptual model and grounded theory were constructed after open, axial and selective coding.ResultsTwenty-four hospital-based physiotherapists were interviewed. Two core themes emerged from the data: ‘puzzle-solving’ and ‘reflecting on decisions’. The third theme—‘relationship between learning, adapting and complexity’—describes how hospital-based physiotherapists’ perceptions of complexity change over time. Complexity as a construct was interpreted as the balance between context and patient-related factors on the one hand and therapist-related factors on the other.ConclusionsHospital-based physiotherapists encounter complexity during performing job-related activities and decision-making. Complexity depends on balancing context and patient-related factors and therapist-related factors. In hospital-based physiotherapy, it was perceived as challenging yet meaningful. Complexity contributes to becoming more competent and, as such, a balance between complex and non-complex activities should be sought for hospital-based physiotherapists.