Objective: Manipulation and mobilization are used to treat neck pain. However, little is known about the diagnostic criteria used to determine the need for manipulation in cases of neck pain. The primary aim of this study was to determine what diagnostic criteria are used to identify which neck pain sufferers should receive spinal manipulation or mobilization. Design: We systematically reviewed randomized controlled trials (RCT) involving mobilization or manipulation for neck pain. A data extraction pro forma was developed and trialled before two independent assessors extracted data sets from each RCT. A descriptive analysis was undertaken. Results: Thirty RCTs met the inclusion criteria. Acute and chronic "Mechanical" neck pain was the most common (43%) diagnosis at recruitment to the RCTs but some (10%) included patients with cervicogenic headache. Clinical criteria were used to determine the need for neck manipulation in over half (63%) of the RCTs. This usually involved exclusion of serious conditions, manual examination for tenderness on palpation, and/or altered vertebral motion in the neck or upper thoracic region which are known to lack validity. The remainder of the RCTs did not report a diagnostic strategy. All RCTs lacked detail descriptions of diagnostic criteria or interventions used. Conclusions: This systematic review highlights the absence of reliable and valid diagnostic protocols to determine the need for spinal manipulation in persons presenting with non-serious, idiopathic, or whiplash-associated (grade II) neck pain. Guidelines requiring the reporting of valid diagnostic criteria are needed to improve the quality of RCTs concerning manual therapy.