The ALS Functional Rating Scale-Revised (ALSFRS-R) is used in the clinic to chart progression and as a primary endpoint measure in clinical trials. In the original description of the scale, evaluations were to be performed by the patient or caregiver, but ratings are commonly performed by health care providers. We determined whether there are differences in scoring based on whether the provider, patient or caregiver performed the evaluation. Overall, all evaluators assessed similar changes in function over time, but significant visit-specific differences were found with higher scores when the patient and provider were the evaluators. We modeled how a change in evaluators at the end of a 9-month trial would influence statistical analysis, if the patient was unable to travel to the study site and the final assessment was performed by telephone. If 25% of the final visit assessments were performed by the patient, in place of the provider, the change in score is less than one point on the ALSFRS-R (-0.7: 95% Confidence Interval -2.1 to 0.3). We conclude that the ALSFRS-R can be successfully used even if evaluators change.