Background: The aim of this study was to compare the therapeutic effects of four methods of ultrasound (US) alone or in combination with low-level laser therapy (LLLT) (L/US), intra (InCI), and extra (ExCI) sheath US-guided corticosteroid injection in the treatment of long head of the biceps (LHB) tendonitis. Methods: In a randomized clinical trial, patients with LHB tendonitis were enrolled in four groups (US, L/US, InCI, and ExCI). Pain using visual analogue scale (VAS) and shoulder performance according to Constant-Murley score (CMS) were evaluated at five visits of before, one week, one month, three months, and one year after treatment. Results: VAS and CMS scores were improved after treatment in all four groups and at all visits in comparison with before treatment. The VAS score in the one-week visit was lower in the InCI group than in all other groups, but it became similar to the score of the ExCI group after this visit and was significantly lower than the score of the US group one year after treatment. CMS was similar at all visits between InCI and ExCI. At one-week and one-month visits, significant differences were seen between the injection groups and the two other non-injection groups, but at the last visit, CMS of the InCI group was only significantly different from that of the US group. Conclusions: Although intrasheath corticosteroid injection under US guidance is an effective method for the treatment of LHB tendonitis, especially in the 1st week after treatment, extra sheath injection also has acceptable results. Using L/US as a less invasive treatment could be as effective as using corticosteroid injection in long-term.