Форма:
$builder
            ->add('email', 'email', array('label' => 'form.email', 'translation_domain' => 'FOSUserBundle'))
            ->add('username', null, array('label' => 'form.username', 'translation_domain' => 'FOSUserBundle'))
            ->add('plainPassword', 'repeated', array(
                'type' => 'password',
                'options' => array('translation_domain' => 'FOSUserBundle'),
                'first_options' => array('label' => 'form.password'),
                'second_options' => array('label' => 'form.password_confirmation'),
                'invalid_message' => 'fos_user.password.mismatch',
            ))

Вьюшка:
{{ form_start(form, {'method': 'post', 'action': path('fos_user_registration_register'), 'attr': {'class': 'fos_user_registration_register'}}) }}

    <div class="form-group">
        {{ form_label(form.email, null, {'label_attr': {'class': ''}}) }}

        {{ form_widget(form.email, {'attr': {'class': 'form-control'}}) }}

    </div>

    <div class="form-group">

        {{ form_label(form.username, null, {'label_attr': {'class': ''}}) }}

        {{ form_widget(form.username, {'attr': {'class': 'form-control'}}) }}

    </div>

    <div class="form-group">

        {{ form_label(form.plainPassword, null, {'label_attr': {'class': ''}}) }}

        {{ form_widget(form.plainPassword, {'attr': {'class': 'form-control'}}) }}

    </div>

    <div>
        <input class="btn btn-primary" type="submit" value="{{ 'registration.submit'|trans }}" />
    </div>
{{ form_end(form) }}