We performed a prospective, observational study using a non-surgical, conservative protocol with immediate mobilization for the treatment of 101 isolated stable or initially unstable proximal phalangeal fractures. The patients were evaluated at the time of discharge from therapy treatment, mean 7 weeks (range 3–15) after conservative treatment. These patients achieved a median proximal interphalangeal joint extension of −4° (IQR 0, −8), a mean total active motion of 253° (SD 20) and minimal pain. We conclude that a non-surgical, conservative protocol can be used for patients with isolated proximal phalangeal fractures without uncorrectable finger rotation or fracture angulation exceeding 25° in the sagittal plane or 10° in the coronal plane following closed reduction. Our data supports that a conservative protocol can be the good option for isolated stable or initially unstable proximal phalangeal fractures. Level of evidence: IV.