The authors evaluated a modified Lapidus technique for 21 rheumatoid hallux valgus deformities. The technique corrects the deformity by performing arthrodesis of the first tarsometatarsal joint and preservation of the first metatarsophalangeal (MTP) joint. The authors clinically studied patients' subjective improvement of pain and footwear comfort, as well as their satisfaction with the outcome of the surgery. The study also analyzed radiographic changes of the hallux valgus angle (HVA) and two intermetatarsal angles, one between the first and the second (M1/2) and the other between the first and the fifth (M1/5). They were measured before the surgery, 3 weeks after the surgery, and at the last follow-up. Pain relief was great or moderate in 17 feet and footwear comfort was improved in 16 feet. Fifteen patients were satisfied or satisfied with some reservations. The average HVA significantly decreased from 44.1 degrees preoperatively to 10.6 postoperatively and significantly increased again to 29.1 at the last follow-up. The average M1/2 and M1/5 significantly decreased postoperatively (from 13 to 8.3 and from 32.2 to 21.1, respectively), and the reduction of M1/2 remained at the last follow-up (8.7), while M1/5 significantly increased again (28.3). This modified Lapidus technique is a useful method for rheumatoid hallux valgus deformity, which can preserve the first MTP joint.