Objectives Biologic disease modifying anti-rheumatic drugs (bDMARDs) have significantly improved the care of patients with rheumatic muscle-skeletal disorders (RMDs). Considering their immunosuppressive action, a theoretical increase of malignancy risk has been a major concern in the last few decades. The objective of this study is to analyze the incidence of malignancies in a cohort of patients affected by rheumatoid arthritis (RA), psoriathic arthritis (PsA), and ankylosing spondylitis (AS) treated with bDMARDs. Methods The charts of bDMARD-treated RMD patients were reviewed, and data about bDMARD exposure and malignant cancers (excluding non-melanoma skin cancer) were collected. Results 921 patients were included (median age: 50.59 years, 66.67% females); 1374 bDMARD treatments were administered, 87.12% were tumor necrosis factor inhibitors. A total of 21 malignant neoplasms were detected in 21 patients (61.90% females, median age at cancer diagnosis: 64.99 years), 66.67% in RA patients, 19.05% in PsA, and 14.28% in AS. Among them, 10 patients (47.62%) were treated with etanercept, 6 patients (28.57%) with adalimumab, and 1 case each with tocilizumab, certolizumab, golimumab, infliximab, and abatacept. The most common malignancies that we found were lung cancers, ductal mammary carcinomas, melanomas, and lymphomas. The incidence rate (IR) of malignancies in our cohort was 3.47 per 1000 person-years (p-y); the higher IRs were in RA patients (5.13 per 1000 p-y), in males (4.21 per 1000 p-y), and in patients aged >70 years (10.14 per 1000 p-y). Conclusions The results of our study showed IR of malignancies in RMD patients treated with bDMARDs that is in agreement with literature data.