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Schizophrenia Spectrum Disorders (SSD) are characterized by cognitive deficits that can significantly impact daily functioning and quality of life. The Subjective Scale to Investigate Cognition in Schizophrenia (SSTICS) is a widely used self-report tool for assessing subjective cognitive impairments. This study validates the German version of the SSTICS. Data from  = 308 participants (38% female) with SSD were analyzed to evaluate factor structure, reliability, and convergent/discriminant validity. A second sample of  = 60 inpatients (37% female) with SSD was used to assess sensitivity to change over a four-week treatment period. The SSTICS and its 14-item short form demonstrated high internal consistency (Cronbach's α = 0.90 and 0.88, respectively) and reliability (McDonald's ω hierarchical = 0.900 and 0.881, respectively). Confirmatory factor analysis supported a five-factor model (memory, attention, executive functions, language, and praxia): Comparative Fit Index (CFI) = 0.97, Root Mean Square Error of Approximation (RMSEA) = 0.08. Strong correlations with the Cognitive Fusion Questionnaire ( = 0.60) and the cognitive domain of the WHO Disability Assessment Schedule 2.0 ( 0.73) supported convergent validity. Low correlations with the cognitive factors of the Positive and Negative Syndrome Scale ( ≤ 0.29) suggest a discrepancy between subjective and clinician-rated cognitive impairments. The SSTICS showed sensitivity to change: minimal detectable change (MDC) = 0.54, though responsiveness was limited: responsiveness ratio (RR) = -0.435. Overall, the German SSTICS is a reliable and valid instrument for assessing subjective cognitive impairments in SSD. The study underscores the relevance of self-reported cognitive difficulties in clinical contexts. Future research should explore associations with objective neurocognitive measures and long-term sensitivity to change.