In research and clinical contexts, it is important to briefly evaluate perceived Psychological and Social Support (PSS) to plan psychological interventions and allocate efforts and resources. However, an appropriate brief assessment tool for PSS was lacking. This study aimed at developing a brief and accurate scale to specifically measure PSS in clinical and emergency contexts, with specific, relevant, targeted, and irredundant items. Experienced clinicians developed the perceived Psycho-Social Support Scale (PSSS) and administered it to a clinical sample (N = 112) seeking psychological help during the COVID-19 emergency. A Confirmatory Factor Analysis examined the PSSS internal structure, and a Multiple Indicator and Multiple Causes model investigated its association with the number of sessions and emotional symptoms. The PSSS showed good psychometric properties and the Confirmatory Factor Analysis provided acceptable fit indexes for a unidimensional structure. The Multiple Indicators and Multiple Causes revealed that more sessions and emotional symptoms were associated with lower PSSS scores. The PSSS is a reliable brief tool to measure PS and could be useful to individualize treatments (i.e., number of sessions) to efficiently allocate efforts and resources in clinical contexts and emergencies (e.g., earthquake, COVID-19 pandemic).