Obsessive-compulsive symptoms are frequent in schizophrenia-spectrum disorders and often cause differential diagnostic challenges, especially in first-contact patients. Drawing upon phenomenology of cognition, we critically review classic and contemporary psychopathological notions of obsessive-compulsive phenomena and discuss their relevance for differential diagnosis between obsessive-compulsive disorder (OCD) and schizophrenia-spectrum disorders. The classic psychopathological literature defines true obsession as intrusions with intact resistance and insight and regards these features as essential to the diagnosis of OCD. In schizophrenia, the classic literature describes pseudo-obsessive-compulsive phenomena characterized by lack of resistance and an affinity with other symptoms such as thought disorder and catatonia. By contrast, the notions of obsession and compulsion are broader and conceptually vague in current diagnostic systems and research instruments. Here, these phenomena overlap with delusions as well as various subjective and behavioral anomalies, which we discuss in detail. Furthermore, we examine a link between obsessive-compulsive phenomena and disturbances of basic structures of experience in schizophrenia-spectrum disorders addressed in contemporary psychopathological research. We suggest that these experiential alterations have relevance for differential diagnosis and early detection in this complex symptom domain.