Background/aim: Medical students often face intense pressure to excel, which can lead to imposterism, characterized by persistent self-doubt and fear of being exposed as inadequate, alongside high levels of perfectionism. This study aims to assess the prevalence of imposterism and perfectionism among medical students in Saudi Arabia and explore their potential implications for student well-being. Methods: A cross-sectional analytical study was conducted between October and December 2024 among female medical students in Saudi Arabia. Data were collected via an online survey, which included demographic questions, the validated Arabic versions of the Clance Impostor Phenomenon Scale (Ar-CIPS), the short form of the Big Three Perfectionism Scale (BTPS-SF), and the General Self-Efficacy Scale (GSES). Results: A total of 265 medical students (mean age 20.96 ± 1.44 years) participated. Most reported a monthly income of less than 2000 SR, and the majority had a GPA above 4.5. A 74.3% expressed moderate impostor experiences. The BTPS-SF revealed the highest scores in self-critical perfectionism, followed by narcissistic and rigid perfectionism. Higher impostor scores were significantly associated with greater perfectionism and lower self-efficacy (p < 0.05). In multivariable analysis, BTPS-SF scores positively predicted CIPS scores (β = 0.52, p < 0.001), whereas GSE scores predicted lower CIPS scores (β = −0.47, p = 0.001). Conclusions: This study revealed a high prevalence of impostor phenomenon and perfectionism among female medical students, with self-critical perfectionism being the most prominent. Imposterism was significantly associated with higher perfectionism and lower self-efficacy.