We consider the long term behaviour of a one-dimensional mixed effects diffusion process (X(t)) with a multivariate random effect φ in the drift coefficient. We first study the estimation of the random variable φ based on the observation of one sample path on the time interval [0, T ] as T tends to infinity. The process (X(t)) is not Markov and we characterize its invariant distributions. We build moments and maximum likelihood-type estimators of the random variable φ which are consistent and asymptotically mixed normal with rate √ T. Moreover, we obtain non asymptotic bounds for the moments of these estimators. Examples with a bivariate random effect are detailed. Afterwards, the estimation of parameters in the distribution of the random effect from N i.i.d. processes (Xj(t), t ∈ [0, T ]), j = 1,. .. , N is investigated. Estimators are built and studied as both N and T = T (N) tend to infinity. We prove that the convergence rate of estimators differs when deterministic components are present in the random effects. For true random effects, the rate of convergence is √ N whereas for deterministic components, the rate is √ N T. Illustrative examples are given.