Objective To compare the clinical effect and safety of manipulation under anesthesia (MUA) using FEAR or simple abduction in patients with primary frozen shoulder (PFS). Methods A total of 70 PFS patients were divided into two groups: a FEAR group (group F) or a simple abduction group (group A), according to the random number table method. The FEAR was used for MUA in group F, and simple abduction was used in group A. MUA was performed under C6 nerve root block, and intra‑articular steroid was injected following MUA in all participants. The shoulder pain and disability index (SPADI) and the passive range of motion (ROM) were measured before operation, and 1, 2, and 4 weeks after treatment. The Patients' Global Impression Change score (GIC) score was recorded 1, 2, and 4 weeks and 3 months after treatment. Furthermore, the incidences of re-MUA and MUA-treatment-related serious adverse events, and other treatments received during the 3-month follow-up period were also recorded. Results There were no statistical differences in SPADI pain score, disability score, total score and passive ROM (forward elevation, abduction, external rotation and internal rotation) between the two groups before treatment and 1, 2 and 4 weeks after treatment (all P>0.05). Compared with those before treatment, SPADI pain score, disability score and total score significantly decreased (all P<0.05), and passive ROM (forward elevation, abduction, external rotation and internal rotation) significantly increased (all P<0.05) 1, 2 and 4 weeks after treatment. Compared with 1 week after treatment, both groups showed decreases in SPADI disability score and total score and group F presented reduced SPADI pain score 2 weeks after treatment (all P<0.05); both groups showed decreases in SPADI pain score, disability score and total score 4 weeks after treatment (all P<0.05); passive ROM (forward elevation, abduction, external rotation and internal rotation) increased in both groups 2 and 4 weeks after treatment (all P<0.05). Compared with 2 weeks after treatment, both groups showed decreases in SPADI pain score and total score and group F presented reduced SPADI disability score 4 weeks after treatment (all P<0.05), and passive ROM (forward elevation, abduction, external rotation, and internal rotation) increased in both groups (all P<0.05). There were no statistical differences in GIC scores between the two groups 1, 2, 4 weeks and 3 months after treatment (all P>0.05). Compared with 1 week after treatment, both groups showed reduced GIC scores 4 weeks and 3 months after treatment (all P<0.05). Compared with 2 weeks after treatment, group A showed reduced GIC scores 4 weeks and 3 months after treatment (all P<0.05). The significant improvement rate (GIC=1) in group F and group A 1 week after treatment was 66.7% and 59.4% (P>0.05), respectively, and the significant improvement rate in both groups during the 3-month follow-up period was 100%. There were no MUA-treatment-related serious adverse events between the two groups, and there were no statistical differences in the number of cases of re-MUA and the number of cases receiving other treatments during the 3-month follow-up period between the two groups (all P>0.05). Conclusions Simple abduction and FEAR have similar clinical effect and safety in the treatment of PFS, when combined with intra‑articular steroid injection.