The present work illustrates the main results of an experiment on errors and repairs in spoken language transcription, with significant relevance for the evaluation of validity, reliability and correctness of transcriptions of speech belonging to several different typologies, set for the annotation of spoken corpora. In particular, we dealt with errors and repair strategies that appear on the first drafts of the transcription process that are not easily detectable with automatic post-editing procedures. 20 participants were asked to give an accurate transcription of 22 short utterances, repeated from one to four times, belonging two non-spontaneous (10) and spontaneous conversation (10). Error analysis suggests a general preference for meaning preservation even after the alteration of the original form, and for the preference for certain error patterns and repair strategies.