Potential contributing factors (PCFs) for irritability of an unknown origin (IUO) in children with neurological conditions are identifiable through structured diagnostics. Uncertainty exists regarding the actual relevance of identified PCFs to IUO. Assessments from parents as well as nursing, psycho-social, and medical professionals were used to determine the contribution of different PCFs in the development and maintenance of IUO. For this, individual PCFs of N = 22 inpatient children with IUO were presented to four raters. Descriptive statistics, Kruskal–Wallis tests, and Krippendorff’s alpha were used to determine which PCFs were most relevant to explain IUO and rater agreement. Psycho-social aspects (44.7%), hyperarousal (47.2%), pain (24.6%), and dystonia (18.1%) were identified as the most relevant PCFs for IUO. Descriptively, physicians’ relevance rating regarding psycho-social aspects, hyperarousal, and dystonia deviated the most from the overall group rating. All professional raters considered psycho-social aspects to be more relevant than did parents. Parents rated pain as more relevant than the other raters. Kruskal–Wallis tests showed no significant differences between relevance ratings (H = 7.42, p = 0.059) or the four parties’ deviations (H = 3.32, p = 0.344). A direct comparison of the six two-party constellations showed that across all factors, agreement was weak to moderate. The highest agreement was between physicians and nurses (α = 0.70), and the lowest was between nurses and psycho-social experts (α = 0.61). Understanding which psycho-social and various biological PCFs are significant for IUO can facilitate more targeted and individualized pediatric palliative care for affected patients.