Objectives and methods: Mismatch negativities (MMN) to frequency and duration changes in a series of repetitive tones and to two different consonant-vowel syllables (ba and ga, standard da) were recorded in a test and retest session in 15 children aged 7–11 years. Reliability within one session and stability between the sessions of MMN amplitudes and the ERP-components P1 and N1 were determined by correlation coefficients. Results: Mean amplitudes of the grand averages showed a decrease of MMN during the second test session in a late latency window (400–500 ms) for the frequency MMN and of the MMN elicited by speech stimuli. The individual stability reached significance only for the duration deviant and one of the syllables. Compared to results found in adults with similar stimulus conditions the stability of the MMN in children seems to be somewhat lower. The components P1 and N1 to both stimulus types (tone and speech), however, showed a high reliability and individual stability. Conclusion: While MMN is a useful tool to study processing deficits in groups of children, as e.g. in language-impaired children, MMN as a individual diagnostic measure should be interpreted very cautiously.