Clinical decision making is influenced by a range of factors and constitutes an inherently complex task. Here we present results from the decisions regarding ADHD management (DRAMa) study in which we undertook a thematic analysis of clinicians' experiences and attitudes to assessment, diagnosis and treatment of ADHD. Fifty prescribing child psychiatrists and paediatricians from Belgium and the UK took part in semi-structured interviews about their decisions regarding the assessment, diagnosis and treatment of ADHD. Interviews were transcribed and processed using thematic analysis and the principles of grounded theory. Clinicians described the assessment and diagnostic process as inherently complicated and requiring time and experience to piece together the accounts of children made by multiple sources and through the use of varying information gathering techniques. Treatment decisions were viewed as a shared process between families, children, and the clinician. Published guidelines were viewed as vague, and few clinicians spoke about the use of symptom thresholds or specific impairment criteria. Furthermore, systematic or operationalised criteria to assess treatment outcomes were rarely used. Decision making in ADHD is regarded as a complicated, time consuming process which requires extensive use of clinical impression, and involves a partnership with parents. Clinicians want to separate biological from environmental causal factors to understand the level of impairment and the subsequent need for a diagnosis of ADHD. Clinical guidelines would benefit from revisions to take into account the real-world complexities of clinical decision making for ADHD.